advice needed - Is it time to intervene?

[Acebird]

My son, who started this adventure, is pondering the split reasoning that we can always unite the split with hive 1 before winter starts.

What kills more hives then varroa is impatience.  You can recombine but it will be weaker then the day you split.  Splitting hives before you know what the hive is capable of doing makes no sense to me unless you have a whole lot of hives.