Hi and welcome afrikat
My ds is 6 months 1 wk & we have done the 90 min thing since about 12 weeks. He is like clockwork, particularly 1st thing in the morning, cannot stay awake for more than 90 mins after waking for the day. 1st nap used to be an hour or bit more, now reduced to 40 mins ish, another nap 90 mins after waking from that, then he might go 2 hrs before the next & the gap between naps gets longer throughout the day.
Have heard it said that the 1st nap of the day is the easiest to introduce changes to as they are most receptive soon after night sleep.
Naps have definitely improved night sleep here. Far more than weaning as the few half spat out spoonfuls he has sporadically eaten are going to have no effect on his appetite. He sat howling in his high chair 3 times today 
Things have got a bit better here, not perfect, but vastly improved, for the moment anyway! I've done nothing different apart from resigning myself to having a reluctant sleeper. Given his recent immense growth spurt, he was waking as he was hungry, I continued to feed ignoring tuts and bosom hoiking from family and at the moment its calmed down. Til the next regression/growth spurt! I just have to stop co sleeping now....ha!
I have been musing about sleep, weaning etc & for every person who swears it has helped, you can find another who swears it hasn't. I don't think its a coincidence that weaning usually occurs around 5-6 mnths and that some babies will just find their own way around that time regardless of what else is going on.