As long as you acclimate them, you can stock them as soon as the ice is gone. However, there is no real advantage to doing this until the water temp is about 60, when they will start spawning.
As a recommendation, once you get your crappies stocked, stock some 4"-5" GSH. They will be too large for your crappie to eat, however their young won't and the crappies will love the secondary food source besides just the FHM... That is if you are just trying to grow monster crappies.
Keep us updated on your experiment!
