Up here in the Great White North, I plant by instinct or I simply get tired of dicking around and stick them in the ground.
Planting though may cover weeks, not days.
I will plant from ground is good to till, till stores selling at clearance prices.
A cold snap will ,for lacking of a better word, stun them and they will sit till they feel like growing and this can happen all through may so waiting for perfect time is an exercise in frustration and pointless.
I will on odd occasions, if they are small enough put something over them for over night protection but as I said, that only happens on odd occasions.
