According to their study messaging etiquette says waiting more than 20 minutes to respond can be seen as rude. ... “After sending a message, the sender experiences increasing anxiety while waiting for a response; a late response can feel like a snub or an indicator of your importance to the receiver.”

Is it attractive to reply late?

Well science says making the other person wait for your reply will increase your attractiveness and it's all down to 'reward uncertainty'. ... Dopamine is a neurotransmitter that helps control the brain's reward and pleasure centre and it's this that gets activated when waiting for that all-important reply.

How long is too late to text back?

Post Senning's general rule is to not wait longer than one to three hours to reply, he tells TI. "A text conversation can go stale in a few hours," he says. "Don't just make them wait." If you're crushing on someone, don't play mind games, he says.