My kids are now 6 and 9.
Ever since they were very young, they napped or had a quiet time.
It was daily routine. It wasn't much of a battle.
BUT per age stages and some days just were not good days, then I as the Mom, amended what went on in the afternoon.
Our nap times or quiet times, were in the afternoon, after lunch.
That was when my kids were TIRED.
Quiet time, for *me*... is them being quiet and doing something quiet. I don't care where in the house they do it. Just as long as it is a more calm quiet thing. AND I also tell them IT IS QUIET TIME FOR MOMMY TOO. Which it was. It wasn't just an excuse or a way to get them to do what I want. It was, MY quiet time too. And we all did it TOGETHER.
That worked for me.
And still does.
I don't force it.
Never had to.
My son, was taking daily naps, until he started Kindergarten. And even in Kinder, they would have nap time there, or he'd do it at home after school. No battles.
I didn't have to force it.
AND the thing is: I was always honest with my kids. I actually told them... they are over-tired, when they get over-tired, they get fussy, when they get fussy it is harder to rest or nap or go to bed. Mommy knows their symptoms...and I taught them too, about it. So then, they KNEW when they were just tired and needed to rest/nap etc. And if I was tired too and needed a break, I TOLD my kids that. And that we ALL... have quiet time. Before Mommy goes crazy.
AND my kids, never could nap or rest, IF they were hungry.
So, rest/naps/quiet time was ALWAYS AFTER, lunch.
AND during lunch, which was before noon, that was ALREADY a time of calm. I set the stage... from lunch time... for naps or quiet time. Already. At lunch time. Then that way, my kids would start to "wind-down" already... and segue... into... nap time or quiet time. Of which I always verbally cued them about what is coming up. But they knew it... like autopilot... because I always did this routine, everyday.
You also have to: verbally "cue" the child. ie: don't say "Quiet time now..." instead say: " after lunch is quiet time. After lunch we get ready." And then after lunch, make things quiet. And then verbally cue the child. Not nag, but verbally coax. Or, let your son.... do what he needs to do to "wind-down." Tell him "Wind down time.... " maybe he wants to do it in a different sequence than you want. So let him.. as long as it is not unreasonable. Everyone has a different sequence of things they like to do, before rest time.
And if he is so slow moving... then for him... you NEED to, start any prep, BEFORE the actual time you want him to do it. ie: if you have to leave the house at 10:00am, don't tell him to get ready at 9:40am. Tell him at least... 1 hour, before you actually have to, leave. You need to leave, a larger turn around time, for him to do things. He does not do well, being "rushed." Or if you want him to go to bed at 8:00pm. Don't start the bedtime routine at 7:30 (bath, pj's, toilet, etc.). do it, 1 HOUR earlier than the actual bedtime.