I have been told the best time to split a hive is before the end of June. The reason for this is that you want both colonies to survive the winter, and the new colony needs to build the comb and gather stores for the winter. And don't expect any honey from either one, as they will both be concidered a new hive.
Of course, when I was told this information, I was living in Idaho.....where the winters are cold and women have hairy legs! and the bees have a hard time surviving the cold.
I now live in a more temperate climate of Oregon....and the winters are much wetter, but it sure beat shoveling snow from the drive way!.
BTW, had to get into my hives this yesterday and found new comb and honey in it on the top bars of my super and inner cover.Scrapped this off as the inner cover was become hard to remove....And the honey was pretty clear...not dark honey. ....You know, honey never tasted so good as when it's your own honey.