When you say you've always had set nap times, do you mean you put your LOs down after the same amount of A time each day or that you put them down at the same actual time each day?
Today she was awake at about 5.45am then went quiet til about 6.10 (not sure she was asleep though). Put her down for her nap at 11.30 as you suggested (she cried a little bit but settled really quickly). She slept til 1.45pm (so 2hrs 15). So I tried to do BTat 6.45 (5 hrs A time, I know you said to aim for 4.5 but didn't quite make it!). She cried when I left the room and kept crying until it escalated and I had to go in. I kept the light off and put my hand on her back and she just kept wriggling around for ages until she eventually started playing. So I assumed she was UT and got her up for just 10mins and all of a sudden she seemed really OT and went down at 7.25. Again she cried but just for a couple of mins.
So, do you think that the first time I tried maybe she'd already been OT but then got a second wind so started acting UT?? I've been keeping a sleep log and I just can't work out the perfect A time in the afternoon especially as she keeps napping for different lengths. Do you think maybe tomorrow night, I should try giving her 4.5hrs and if she doesn't go down, give her another 10mins, try again and if that doesn't work, I'll definitely know she's UT (as usually a second attempt always works)?
God, I feel guilty saying it but I'm finding it really tough constantly over-analysing her BT, A time, nap time, UTness, OT ness..... Usually I manage to solve any sleep hiccups within a week or so (with this website's help!) but this one just seems to keep going....