This past week the sun's been out and my bees have surprised me with the nectar they been bringing in.
I added suppers today. If you want to make a split, can do anytime now.
If you want to hold off, then put the heaviest box on the bottom of the two,
then add a supper on top of the stack.
Then split later as you want.
They'll move honey from under the brood to the super above the brood,
drawing out the wax. This gives them something to do and keeps them busy while also giving them room to store above the brood nest. This will make them not even think about swarming, but will get to work with greed and room to store. You can make your split later as you wish and will maybe have a super of early honey.