More sympathy from me too, Ledkr 
Personally, I found that as long as I got a minimum of 4 hours in one stretch I could survive, so 8 hours in one-hourly increments would have killed me tbh hence the co-sleeping and babies helping themselves to a feed overnight while I semi-snoozed through.
Anyway, yes, with a 4 yo I'd persevere with the concept of the GroClock or the bunny ear one. In fact, we used an old radio alarm clock for DS3 whose getting up time became earlier and earlier when he was around that age. I cracked when he started insisting it was getting up time before 5am
We taught him what a number 7 looks like and he was to stay in his bed/his room until at least 7am. It worked once we had also pointed out to him where the number 7 was to be…. 4.37am did NOT count!
I agree there should be NO baking or any other fun activity on offer that time in the morning.
You know that technique for bedtime that involves just taking them back to bed with less and less input, no eye contact, no fuss? Could you try that in the morning??
I hope you have
and
and
later on.
My worst sleeping is now 12 and has just started sleeping like a teenager
- 12+ hrs per day, every day!