We also did 3,5h cold turkey 2 weeks ago. With 2h awake time you should have 1,5h naps on 3,5 EASY. we started from 1:45A and 1:45S, but quickly went to ratio 2:00-1:30. Right now we are on 3:45 space between morning feeds and I am waiting patiently when DS will be ready for 4h. Right now he is waking from his naps after 1:30-1:45 because of hunger.
If first/second nap is shorter, I let/help DS lengthen next nap/naps to 2h max. Generally after one short nap, he almost always take 2h on second nap. I kept normal A or even +15min between S because for DS E in the middle of activity lengthens awake time and also activity before E is always low key/resettling so he is not so tired as after normal A.
If you still have last nap ended before 5pm I would go for earlier bedtime, so ie 7:00 instead of 7:30. If your last nap will end even earlier, you may go for short 15min catnap around 5/6pm (so 4th nap) and adapt BT according to your kid.
What I stick to is E time, so not to feed him earlier so even if naps are mess try to keep 3,5 eating patern and so he learns the rule.
HTH