Mine are usually out for potty break at fifty degrees. Lower temperature if they are wrapped in tar paper. The tar paper sometimes makes the hive too warm, fools them into flying to their death.
I have seen my bees flying and bringing back pollen at 43 degrees. Last week was mostly in the 50's and it looks like a major flow in on. I know that maple is starting to bloom but I am seeing several different colors of pollen. Jim