Tonight is used to refer to the evening of today or the night that follows today. I'm at home tonight. Tonight, I think he proved to everybody what a great player he was. There they will stay until 11 o'clock tonight.

When can you say tonight?

'Tonight' generally covers the whole evening and night (as a continuation of the evening): 'Let's go clubbing tonight and then watch the sunrise'. 'I hope to sleep well tonight' is idiomatic, but if you were describing something that explicitly starts after midnight you probably would not say tonight.

What does tonight mean?

: the present night or the night following this present day.