@robwebb We had the same issue of super late bedtimes to accommodate the second nap and it was throwing everything off, around the same age too. She also wasn’t napping well, and now that she’s on one nap she naps for longer than with two total. She is about a week shy of 18 months and this has been our schedule since ~14 months.
7 am wake (sometimes 7:15-7:30 but this is rare, I do let her sleep in if she wants to though, I didn’t when she was on 2+ naps)
12:15-2:15 nap
7:15 bed but is asleep around 7:45 (I’ve tried everything and just have figured out that she needs the extra time to wind down, this probably wouldn’t apply to you.)
She ends up with about ~13 hours of sleep per day