On the contrary, it's actually fundamental to your question, really
I'd disagree. For me there is something about the last few full days before "long time till I actually clap eyes on you again" starts again. They are more precious. They mean more to me than at the start of the visit when I feel like time is on my side.
I think what is more relevant is frequency. If somebody can pop over several times a year then the tail-end of one visit doesn't herald a long absence. But if you only see each other infrequently, well that can feel different.
Especially with kids, because by the time the next visit comes around they have changed so much. It matters maybe more for gran than the kids I think. This might be the last couple of days she has left to drink in her grandchild at 5. Becuase by the time she comes back ... 5 has long gone.
I have only my sister and BIL, and they are younger than me, but I think perhaps if it was a question of an older relative, I'd also be aware that there were no guarentees that grannie would be in the same fine fettle and be able to do so much next time. I think that might give me an even greater sense of urgency to squeeze every last drop out of the time left before time and distance seperated everybody again.
School is very important to me. I have gone to considerable lengths (and gained many grey hairs) to get my son access to a decent education. But all the same a day or two of being in school doesn't trump everything else for me. The connections we have with the people we love matter too, and I don't think it's anti-education to very occasionally place the priority on those connections, when we can, while we still can.