How bug are they now? How much space do you have? Are they at least half the size you want them to end up being?
If they sprouted the end of March, then they should be alright to flip in the next week or two. You could go now if you wanted, but not knowing size or seeing pics, we're just speculating.
If they sprouted the end of March, then they should be alright to flip in the next week or two. You could go now if you wanted, but not knowing size or seeing pics, we're just speculating.