I'd probably try a really early BT like 6pm it could all be OT behaviour built up. If you get a 11.5/12 hour night then that's good solid sleep to build the next day on, or you could pop a cat nap in around 3pm say 20 mins and stick to 7pm BT.
Sometimes it's just developmental stuff going on that we can't fix or find a reason for and it just resolves itself.
My DS1 is 4.5 and hasn't napped since he was 3 but he still had 6.30 BT once in a while if we've been busy or he's had a disturbed night.