May is the time for divides. Strong overwintered colonies should be divided or they will more than likely swarm. If your bees swarm, the likelihood of getting any surplus honey off the colony that swarmed, is very low. Just because your colony overwintered does not mean you can divide it.
Dividing a colony of bees can happen when you have eight frames of brood and bees in your hive. The definition of brood is frames of bees covered both sides with bees and each of the eight frames has eggs, open larvae, or capped brood. The eight frames of brood is the total needed to divide. The frames of brood will be spread out throughout the colony. Example, if you are in a two or three deep colony you may have five frames of brood in the top box, three frames of bees in the lower box. You equalize the brood out between two boxes. Because when the divide happens you never know where the queen is.
This is a link to Gary's from the Univ of MN homepage. He describes how to divide.
How to do a divide