• From milliseconds:

  var millis = 978296400000;
  var dt = DateTime.fromMillisecondsSinceEpoch(millis);
  
  // 12 Hour format:
  var d12 = DateFormat('MM/dd/yyyy, hh:mm a').format(dt); // 12/31/2000, 10:00 PM
  
  // 24 Hour format:
  var d24 = DateFormat('dd/MM/yyyy, HH:mm').format(dt); // 31/12/2000, 22:00
  

• From Firestore:

  Map<String, dynamic> map = docSnapshot.data()!;
  DateTime dt = (map['timestamp'] as Timestamp).toDate();
  

• Converting one format to other:

  • 12 Hour to 24 Hour:

    var input = DateFormat('MM/dd/yyyy, hh:mm a').parse('12/31/2000, 10:00 PM');
    var output = DateFormat('dd/MM/yyyy, HH:mm').format(input); // 31/12/2000, 22:00
    

  • 24 Hour to 12 Hour:

    var input = DateFormat('dd/MM/yyyy, HH:mm').parse('31/12/2000, 22:00');
    var output = DateFormat('MM/dd/yyyy, hh:mm a').format(input); // 12/31/2000, 10:00 PM
    

_{Use intl package (for formatting)}

Full code for anyone who needs it:

String readTimestamp(int timestamp) {
    var now = DateTime.now();
    var format = DateFormat('HH:mm a');
    var date = DateTime.fromMillisecondsSinceEpoch(timestamp * 1000);
    var diff = now.difference(date);
    var time = '';

    if (diff.inSeconds <= 0 || diff.inSeconds > 0 && diff.inMinutes == 0 || diff.inMinutes > 0 && diff.inHours == 0 || diff.inHours > 0 && diff.inDays == 0) {
      time = format.format(date);
    } else if (diff.inDays > 0 && diff.inDays < 7) {
      if (diff.inDays == 1) {
        time = diff.inDays.toString() + ' DAY AGO';
      } else {
        time = diff.inDays.toString() + ' DAYS AGO';
      }
    } else {
      if (diff.inDays == 7) {
        time = (diff.inDays / 7).floor().toString() + ' WEEK AGO';
      } else {

        time = (diff.inDays / 7).floor().toString() + ' WEEKS AGO';
      }
    }

    return time;
  }

Thank you Alex Haslam for the help!

If you are using firestore (and not just storing the timestamp as a string) a date field in a document will return a Timestamp. The Timestamp object contains a toDate() method.

Using timeago you can create a relative time quite simply:

_ago(Timestamp t) {
  return timeago.format(t.toDate(), 'en_short');
}

build() {
  return  Text(_ago(document['mytimestamp'])));
}

Make sure to set _firestore.settings(timestampsInSnapshotsEnabled: true); to return a Timestamp instead of a Date object.

if anyone come here to convert firebase Timestamp here this will help

Timestamp time;
DateTime.fromMicrosecondsSinceEpoch(time.microsecondsSinceEpoch)

To convert Firestore Timestamp to DateTime object just use .toDate() method.

Example:

Timestamp now = Timestamp.now();
DateTime dateNow = now.toDate();

As you can see in docs

meh, just use library; it does all the heavy-lifting for you.

EDIT:

From your question, it seems you wanted relative time conversions, and the timeago library enables you to do this in 1 line of code. Converting Dates isn't something I'd choose to implement myself, as there are a lot of edge cases & it gets fugly quickly, especially if you need to support different locales in the future. More code you write = more you have to test.

import 'package:timeago/timeago.dart' as timeago;

final fifteenAgo = DateTime.now().subtract(new Duration(minutes: 15));
print(timeago.format(fifteenAgo)); // 15 minutes ago
print(timeago.format(fifteenAgo, locale: 'en_short')); // 15m
print(timeago.format(fifteenAgo, locale: 'es'));

// Add a new locale messages
timeago.setLocaleMessages('fr', timeago.FrMessages());

// Override a locale message
timeago.setLocaleMessages('en', CustomMessages());

print(timeago.format(fifteenAgo)); // 15 min ago
print(timeago.format(fifteenAgo, locale: 'fr')); // environ 15 minutes

to convert epochMS to DateTime, just use...

final DateTime timeStamp = DateTime.fromMillisecondsSinceEpoch(1546553448639);

Just make sure to multiply by the right factor:

Micro: multiply by 1000000 (which is 10 power 6)

Milli: multiply by 1000 (which is 10 power 3)

This is what it should look like in Dart:

var date = new DateTime.fromMicrosecondsSinceEpoch(timestamp * 1000000);

Or

var date = new DateTime.fromMillisecondsSinceEpoch(timestamp * 1000);

How to implement:

import 'package:intl/intl.dart';

getCustomFormattedDateTime(String givenDateTime, String dateFormat) {
    // dateFormat = 'MM/dd/yy';
    final DateTime docDateTime = DateTime.parse(givenDateTime);
    return DateFormat(dateFormat).format(docDateTime);
}

How to call:

getCustomFormattedDateTime('2021-02-15T18:42:49.608466Z', 'MM/dd/yy');

Result:

02/15/21

Above code solved my problem. I hope, this will also help you. Thanks for asking this question.

Assuming the field in timestamp firestore is called timestamp, in dart you could call the toDate() method on the returned map.

// Map from firestore
// Using flutterfire package hence the returned data()
Map<String, dynamic> data = documentSnapshot.data();
DateTime _timestamp = data['timestamp'].toDate();

I don't know if this will help anyone. The previous messages have helped me so I'm here to suggest a few things:

import 'package:intl/intl.dart';

    DateTime convertTimeStampToDateTime(int timeStamp) {
     var dateToTimeStamp = DateTime.fromMillisecondsSinceEpoch(timeStamp * 1000);
     return dateToTimeStamp;
   }

  String convertTimeStampToHumanDate(int timeStamp) {
    var dateToTimeStamp = DateTime.fromMillisecondsSinceEpoch(timeStamp * 1000);
    return DateFormat('dd/MM/yyyy').format(dateToTimeStamp);
  }

   String convertTimeStampToHumanHour(int timeStamp) {
     var dateToTimeStamp = DateTime.fromMillisecondsSinceEpoch(timeStamp * 1000);
     return DateFormat('HH:mm').format(dateToTimeStamp);
   }

   int constructDateAndHourRdvToTimeStamp(DateTime dateTime, TimeOfDay time ) {
     final constructDateTimeRdv = dateTimeToTimeStamp(DateTime(dateTime.year, dateTime.month, dateTime.day, time.hour, time.minute)) ;
     return constructDateTimeRdv;
   }

Simply call this method to return your desired DateTime value in String.

String parseTimeStamp(int value) {
    var date = DateTime.fromMillisecondsSinceEpoch(value * 1000);
    var d12 = DateFormat('MM-dd-yyyy, hh:mm a').format(date);
    return d12;
}

Example: if you pass the TimeStamp value 1636786003, you will get the result as

11-12-2021, 10:46PM

If you are here to just convert Timestamp into DateTime,

Timestamp timestamp = widget.firebaseDocument[timeStampfield];
DateTime date = Timestamp.fromMillisecondsSinceEpoch(
                timestamp.millisecondsSinceEpoch).toDate();

I tested this one and it works

// Map from firestore
// Using flutterfire package hence the returned data()
Map<String, dynamic> data = documentSnapshot.data();
DateTime _timestamp = data['timestamp'].toDate();

Test details can be found here:

All of that above can work but for a quick and easy fix you can use the time_formatter package.

Using this package you can convert the epoch to human-readable time.

String convertTimeStamp(timeStamp){
//Pass the epoch server time and the it will format it for you 
   String formatted = formatTime(timeStamp).toString();
   return formatted;
}
//Then you can display it
Text(convertTimeStamp['createdTimeStamp'])//< 1 second : "Just now" up to < 730 days : "1 year"

Here you can check the format of the output that is going to be displayed: Formats

Timestamp has [toDate] method then you can use it directly as an DateTime.

timestamp.toDate();
// return DateTime object

Also there is an stupid way if you want really convert it:

DateTime.parse(timestamp.toDate().toString())

Print DateTime, TimeStamp as string from Firebase Firestore:

      Timestamp t;
      String s;
      DateTime d;
//Declaring Variables
      snapshots.data.docs[index]['createdAt'] is Timestamp
                                    ? t = snapshots.data.docs[index]['createdAt']
                                    : s =
      snapshots.data.docs[index]['createdAt'].toString();
            
                                //check createdAt field Timestamp or DateTime
      snapshots.data.docs[index]['createdAt'] is Timestamp
                                    ? d = t.toDate()
                                    : s =
                                        snapshots.data.docs[index]['createdAt'].toString();
            
                                print(s.toString()); //Print Date and Time if DateTime
        print(d.toString()); //Print Date and Time if TimeStamp

Assuming you have a class

class Dtime {
  int dt;
  Dtime(this.dt);

  String formatYMED() {
    var date = DateTime.fromMillisecondsSinceEpoch(this.dt);
    var formattedDate = DateFormat.yMMMMEEEEd().format(date);
    return formattedDate;
  }

  String formatHMA() {
    var time = DateTime.fromMillisecondsSinceEpoch(this.dt * 1000);
    final timeFormat = DateFormat('h:mm a', 'en_US').format(time);
    return timeFormat;
  }

I am a beginner though, I hope that works.

Long num format date into Calender format from:

var responseDate = 1637996744;
var date = DateTime.fromMillisecondsSinceEpoch(responseDate);
//to format date into different types to display;
// sample format: MM/dd/yyyy : 11/27/2021
var dateFormatted = DateFormat('MM/dd/yyyy').format(date);
// sample format: dd/MM/yyy : 27/11/2021
var dateFormatted = DateFormat('dd/MM/yyyy').format(date);
// sample format: dd/MMM/yyyy : 27/Nov/2021
var dateFormatted = DateFormat('dd/MMM/yyyy').format(date);
// sample format: dd/MMMM/yyyy : 27/November/2021
var dateFormatted = DateFormat('dd/MMMM/yyyy').format(date);
print("Date After Format = $dateFormatted");

String readTimestamp(int timestamp) {
    var now = DateTime.now();
    var format = DateFormat('HH:mm a');
    var date = DateTime.fromMillisecondsSinceEpoch(timestamp * 1000);
    var diff = now.difference(date);
    var time = '';

    if (diff.inSeconds <= 0 || diff.inSeconds > 0 && diff.inMinutes == 0 || diff.inMinutes > 0 && diff.inHours == 0 || diff.inHours > 0 && diff.inDays == 0) {
      time = format.format(date);
    } else if (diff.inDays > 0 && diff.inDays < 7) {
      if (diff.inDays == 1) {
        time = diff.inDays.toString() + ' DAY AGO';
      } else {
        time = diff.inDays.toString() + ' DAYS AGO';
      }
    } else {
      if (diff.inDays == 7) {
        time = (diff.inDays / 7).floor().toString() + ' WEEK AGO';
      } else {

        time = (diff.inDays / 7).floor().toString() + ' WEEKS AGO';
      }
    }

    return time;
  }