I'm starting to notice that the kids are at their worst on "transition day," which happens 3 times a week given our current "2-2-3" custody arrangement. My growing "gut-sense" is that fewer changes would be better for them (no changes would be ideal but as we all know, that didn't work out), but I have no solid proof. Many people have asked about a week-by-week arrangement, but dad wouldn't even consider testing a trial period, so that's off the table for now.
It's different for me: the first night away from them is glorious; the second, not at all.
Between school schedules, holidays, summers and general life, I'm not sure there ever really will be a "regular" routine. "Change is constant" they say about parenthood, in all circumstances. No more so than now.