Changing time zones must be such a pain
So basically, you're trying to shift 1.5h, right? I suspect there are lots of opinions on this! I personally like to do daylight savings changes very slowly if possible, my 5yo can cope with bigger jumps now but when my LOs have been younger they've needed gradual changes. So I guess I'd lean towards doing it slowly in your case, since you're only shifting 1.5h, as opposed to, say, 5h.
At least though, whatever happens, you know roughly what to aim for on your return, once he's caught up with OT. I'm sure there used to be a FAQ on adjusting between time zones, I'm going to ask/dig around for it...