Hi Sima,
He doesn't cope very well if his nap is shorter than 1 hour , he tends to have a very short fuse by evening time. As for his morning A time he can handle about 6 -6.5 hours (on a good day), anything over that he'll start to get to meltdown stages, and refuse his nap. If he's sick or teething that A time goes down to about 5 hours... I just watch him to see how he's coping. Yes on EW, it is harder for him to stay up for his nap.. but i take him out so he's distracted then when he gets home and has a snack, read a book then nap time. I assume that he'll have a longer nap if he needs one... He goes down well usually at night, even after EW. If he's really tired he just falls asleep quicker. In those horrid hours of 5-7pm we just keep him quiet with quiet play like puzzles, books and if we are frazzled he watches his show on TV.