We went for 6.30pm which was the earliest we could do in the end, he was in pretty good spirits all day and it actually DID take him a while to go to sleep (30 mins) which I think was UT, not OT as he was happy enough.
I think 11.5hrs ONS is pretty good too! That's what we get on a really good night, and our nap is pretty much gone. I guess you could cap the nap a little shorter, see if that gives you a bit more ONS.... but 13hrs TS would be like winning the lottery here! ;-) Each kid is different though, of course....
Would love to work out a formula that works for a bit of consistency here still - confusing much!!!??!!