What is a reasonable time for your boyfriend to not reply back?

I’m really trying not to be toxic or crazy but on his days off he does not reply back until the night. We have always had big problems and broken up before because or communication problems.

Today he is off. I wrote to him this morning at out 12pm. As of now it is 5pm and he still has not replied back.

Wha time do you find acceptable to not reply back? Honestly more than 4 hours is unacceptable especially if you’re off that day.

Honestly that triggers the crazy in me especially if he sees my story during that time period and still does not reply back.