Along with the "timing" you also have to take onto consideration that you have to follow your ds's cues too. We have to tweak with a 5-6 hours awake time before nap because some days ds is extremely tired by 4.5 hour mark (then we have to do a 5 hour stretch) and some days he's singing, dancing and hyper at the 5.5 hour mark (those days we go for a 6 hour activity period). I always take in consideration 30 mins before the nap to have enough time for winding down, diapering, etc (that can take ages with a squirming toddler LOL). On days he's ill or teething, he's more likely to be tired on shorter stretches and i just go with the flow because if i try to hold him for longer, then he gets overtired and the sleep craziness starts.
To give you some peace of mind, my lo also wakes very late (never before 830 am, mostly 910 am) and his average nap time goes from 220 to 245 pm till 445 (i wake him no later than this if he hasn't woken by his own) and it's a 9-930 pm bedtime...i know it sounds super late for some of you but here in Mexico timings are different and no one goes to bed at 7 pm, it's just how it works, most nurserys open at 9am because of that. Tracy suggested 7-7 timings but also was a big advocate to follow family's lead and dynamics.
So i'd suggest you to observe your lo to see what time suits him best to go down.If you don't want him to go down for nap so late or can't manage to keep him super busy to wear him out, you'll have to start tweaking his schedule, waking him earlier in the morning in 15 mins increments till you get the timings you wish. HTH!