I've always done mine in the morning because that's my FS's preference, but almost all of the americans I speak to do theirs at night. I'm not sure if it affects the interpretation of your monitoring results so it might be worth mentioning it to your Dr just in case?

My FS is very relaxed about the "same time" thing. I tend to stick fairly religiously to doing them exactly 24 hours apart but in the past I've occasionally freaked out because I've done one late and he always dismissed any concerns I expressed. These days I wouldn't stress over doing it 1.5 hours late. I think you should be fine if you just enjoy the performance and do it after. But, again, check with your Dr if you're concerned.