When I lived near a school, I did try to avoid 3-4pm when it was pick-up time. Around here, I'm not that near a school and lots of kids seem to arrive home by bus or bike - or if they're in cars, they're indistinguishable from the other traffic.
I don't have fixed times/routes either, so I try to schedule things so I don't need to ride busy roads on a Friday evening rush hour because that's when I think it's more trouble as the rush seems to be more spread out, with some places finishing early and other groups of people staying for a drink and then the start of weekend-away tourists passing through to the coast (well, not so much this time of year). I don't mind the roads being quiet, and I also don't mind them being jammed (I use the cycle lanes to bypass jams) but it's that heavy-but-fast-moving which seems more troublesome. Don't get that on Mondays here.