I have been asked this question many times of late.
I think anyone who was on the April 11th load should have put on a second box a week ago. The folks who were on the April 25th delivery are almost done drawing comb in the first box. I think by next Wed. or so, another box could be added.
Remember if you are drawing out foundation there has to be feed on the colony at all times.
Hive populations are growing. Foundation will be drawn out at a faster rate now. The bees will use a little more sugar water with the added bees.
Now that the dandelions and fruit bloom is over there will be a dearth in nectar coming in. This will usually kick off the swarming impulse in strong overwintered colonies with older queens. Check strong colonies for swarm cells.
Watch the food in the colony so the bees don't starve.
The next major nectar flow will be the first hay crop. Alfalfa should start blooming in early June. The lack of water may hinder this date.