He's exhausted by 8, fussy, and falls asleep in 2 seconds but I can try
This is why he's waking so early though - you could push more gently, say 15min per week for a bit and see how he goes. Nursery might be a bit happier with that if you talk them through the plan?
PUPD is not appropriate to use when he's not got a suitable routine.
I imagine you're trying to move to something like this:
7 - WU, eat
8 - solids
10 - nap
11:30 - eat
12:30 - solids
2:30 - nap
4 - eat
6:30/7 - eat
7/7:3- BT
The issue with doing it in 15min increments over 4-8 weeks (depending on cooperation from nursery) is that he'll be ready for another change by then and you'll likely spend most of that time in an UT/OT loop which will come with its own NWs and OT building. I don't think the fundamental issue is independent sleep at this point - nobody can be expected to sleep at times they're not tired enough and frankly, he's sleeping UT 1hr naps every time - either he's being woken due something at 1hr every time or he's UT when he's going down for his naps. When DS was in daycare, his carers often mistook his cues - bored for tired, tired for hungry. It really took giving them a routine and asking them to stick to it for things to come out in the wash. It only took 3-4 days once they did it - took me 2 months to convince them.
Would you be able to try an EBT to see if he catches up and copes better?