My boyfriend works in other places, and he always doesn't reply in time when I send messages. How to make him happy and send me a message?

You'd better choose a time convenient for him.

Try not to disturb him during working hours. Lunch or after work is a good time to send text messages.

If you disturb him when you are not at work, he will think that you are very sensible and considerate.

Maybe, when he is not busy, he will send you a message on his own initiative.