Eight weeks after the first full moon that follows the vernal equinox. So a week after Pentecost. Or when the fixtures come out, whichever comes first.
I would go with any of these When players contracts are up and signings begin. when the new fixture list is out. when the players report to their clubs to begin training/friendlies.
Re: I would go with any of these Dreaded day teams move divisions on BBC Sports pages. Or could say 18 June fixtures out. Fair to say close seasons for a couple more weeks yet at least
July 1st. Players contracts tend to run until June 30th & then the day after is the start of the new season