15 month nap nightmare!

[FaintlyMacabre]

Hello, any thoughts or advice very welcome here!

Until a few weeks ago, my DS was in a daytime routine of sorts (we are very much 'go with the flow' type parents and this is the pattern he eventually seemed to settle in).
He would wake at 7ish
Nap at 9ish for 30-45 minutes
After lunch nap for about 1.5 hours at 1-2ish
Bed at 7.30ish.
We co-sleep, he would sleep in his cot in the evenings and then come into bed with us when we went to bed at about 11.
(sorry about the vague times but this was never set in stone).
Anyway, this was going well until recently, when he started to try to drop his morning nap. I thought that he would just have one long sleep -maybe 12-2 or something like that.
However, what has actually happened is that the day has been just pushed forward by about 2.5 hours.
He now has a short nap at 1130 or so, then wants his afternoon nap at about 4, 5 or even 6!
Any attempt to 'trick' him into an early bedtime by keeping him up in the afternoon and then putting him to bed at 6:30 or so backfires -he just treats this as his afternoon nap, sleeps for 2 hours and is then up and ready to play until about 11:30.

This is starting to get to me a bit - I just want some evening time back!
I have no idea of how to go about changing this - the original routine, which suited us well, was something we arrived at very gradually so I had no 'method' of getting there.

Can anyone offer any advice/suggestions?

Does he still wake up at 7?

FWIW DS had a nap at 5 til 7 and would then go to bed at 9:30. Could this work?

Gosh, that sounds awful. We've just gone through the whole 2 naps to one nap thing with my DS (17 mo), and tbh his whole schedule went a bit haywire for a while but has now settled down to some extent. So it may just be that you have to wait it out for a couple of weeks.

My only advice would be not to let him sleep after 4pm no matter how tired they are - we did a couple of times and it buggered up bedtime completely. And stick to the same bedtime each night - it will mean that he will eventually fall into a regular schedule.

See i had to let him nap at 4-5 ish cos he just wouldn't last til later. He would have slept through but then would have been up at 3 so i woke him up at 7 and let him go back at 9:30.

DS was tricky in this transition as well.

If he fell asleep in the morning then I would let him have five minutes max -- often just waking him after a couple of minutes. He would then be just refreshed enough to keep going til after lunch then I would put him down at 12.30-1ish and he would (usually) take a longer nap then that would get him through to bedtime.

Any longer than five minutes in the morning, and he wouldn't go down after lunch. As time went on eventually he stopped needing the morning catnap.

Thank you everyone for the advice! It's good to know we're not alone in this (well, sort of).
I think I'll be trying a mixture of your suggestions -not letting him sleep past 4pm is key, I think, however hard it might be! And having a tiny nap in the morning to keep him going until his afternoon nap sounds good too.

I think that probably it is going to be mostly about waiting it out though -we'll find a new routine eventually.