Hi Honey,
I think in order to get your head around this you may have set WU and BT.
The day he STTN was a longer day by 30 minutes, 12.5 hours with a 1 hour 45 minutes nap. The next day his nap was slightly shorter and his day was 12 hours. Yes, that may seems 'similar' but that slightly change in nap and 30 mins difference at BT can make all the difference. When you're in this kind of mess (and trust me we have been) you can either adjust the day depending on nap length, or you can set WU and BT. IME adjusting BT can often pay off, but if it doesn't then it is harder to draw conclusions as to what is going to work, does that make sense
So in the end on advise of BW, after tweaking BT like a crazy woman and looking at endless routines I had recorded, I took that advise. It can be hard at times to get LO through to BT, but what I believe is really beneficial about it (at this age especially) is that it gives your LO a chance to reset their body clock YK
Also for me, taking the guess work out of it helped me stress a lot less.
Something which was also beneficial to me was to understand that OT is accumulated over time, but UT is something that you get for the day. So even though LO seems really OT, often shortening the day can result in problems too, making it pretty much impossible to decifer between the 2 when it comes to WU's etc. Does that make sense
So if he is up at 6.30 I would go with this:
WU 6.30
Nap midday (uncapped)
BT 7.00
Stick with it and see where you are in a week or so. I would keep a record and see what it looks like at the beginning and the end of the trial.
What do you think