NOTE: I have updated this 2016 post in order to make it appear closer to the other mason bee information
The time to put out your mason bees which have been overwintered in your refrigerator is when you need them to do their work. I release mine in batches. The first batch was several weeks ago when the peaches and nectarines were in bloom. This week, the pears, plums and cherries are in bloom so I just put out another batch of cocoons near my bee homes. I will save the last batch for my apple trees which bloom later.
I had to transplant this peach tree this year to the corner of the vegetable preparation building so I found another good spot to place a bee home.