The hive population is growing quickly; for existing hives from last year, they may already be at 80% of their strength, new hives will be building comb as fast as they can.
For new hives, keep feeding the bees (either honey or sugar syrup) as they need all the feed they can get to draw out the comb. Without the feed, you hive won't be able to produce any surplus honey - keep feeding them till they
stop taking it or until you put the first honey super on.

For existing hives from last year, it is critical that you monitor and add supers as needed otherwise your hive will swarm. When inspecting, look for swarm cells on the bottom of frames. Remove them if you can but your best
bet is to monitor and add supers before they feel congested. Also check your ventilation; inadequate ventilation (too hot) can cause them to swarm.

Bee a Beekeeper