I don't see why it shouldn't be at a convenient date to the organisers, taking local conditions such as weather into consideration. If someone else complains and says it should be such and such a date and can't be moved, then they should volunteer to put on the event. I think the date should be up to those who have kindly volunteered to organise the event.
Wasn't it you who originally suggested here that Finland should be moved to a later date when it "is a bit warmer"? So I guess you're part of the mystery organizing committee then ;) Every Finn knows that it might just as well NOT be much warmer in May, June or July either - you can plan whatever you want & hope fot the best but the weather will be whatever it will be, so there's really no point in dwelling on this weather issue. I also recommend that we let the organizers plan their thing and tell us about it whenever they're ready.