Since 8:30 is probably the latest am nap time you want with a 5am wakeup, I think you have a couple options.
1. Let him sleep until 11AM so that you could push his pm nap to 2, 2:15 even, and BT at 6:30/6:45.
2. Do a hard push for pm nap at 2, BT 6:30/6:45.
3. Split the extra time between PM nap time and BT- NAP 2 at 1:45, BT at 6:15 and add 5-10 mins every few days to get closer to a 7pm BT.
He actually might be a little UT for his pm nap, and 10-15 mins later kight help him. We won't know for aure until we try of course. Which do u think he would handle the best? And remember, if something doesn't work after 2-3days, we can always try another method. I realize you'll be exhausted in the meantime but we'll getthere!
Once his morning wake up time moves out, you can start pushing out the morning nap for a goal of 9:30 (from my experience reading/hearing others' lo at this stage).