Why pollen patties should be on packages until June

I do tell beekeepers to keep pollen patties on until June for a couple reasons.

1. If the weather turns cold and rainy the bees will still be able to have pollen available to feed their brood.
2. A package starts with around 5000 - 2 lb or 7500 - 3 lb bees. The queen starts laying in about 5 - 7 days. New brood goes through their life cycle that take 21 days for the first bees to hatch out. It is another 22 days before the new bees can fly. So that is about 50 days before the new bees can start collecting pollen. That puts us at around June 1st to June 7 before the new bees can forage. There is a growing numbers of bees in the hive but no foragers. Pollen patties need to be available at this crucial time of hive expansion.
3. The bees that came in the package, their numbers are dropping everyday as they are getting older. The numbers of foragers will be dropping before new foragers take their place.
4.  The fruit bloom going on right now, gives the hive an opportunity to large amounts of high quality pollen. The fruit bloom starts to wane around the third week of May. From the end of the fruit bloom until around June 10th or so there is a dearth of pollen. 

Pollen patties helps the hive keep expanding. Sometimes the bees devour them, sometimes they go undisturbed. Keeping pollen patties on is cheap insurance that the hive is kept moving forward and expanding as the honey flow starts around June 15th to 20th.