I am sorry you’re having a hard time. It is not your job to convince, your son needs structure, schedules and routines. It is up to you to give him a routine that includes rest time. If he gets upset, that’s ok but this may help… let him know it’s rest time, but have him choose a game you can play together when the timer goes off. And set the timer together and put the game somewhere he knows where it is. He wil rest and look forward to your time together. Let me know how it goes.
I put on a movie and we chill on the couch watching movie together until I need to get up and make dinner. Usually we’ve had an all day out so the movie is the first time for screen time that day, and he’s tired but he won’t nap past 3.5yrs