Early-mid June is the time of year where most education systems have exams, so in general that is just a really bad time to host an event. Vacations or at the very least regular weekends are better.
Friday 12 or Sat 13 are the best alternatives for me if June 20+ doesnt' work. I could probably join if it's hosted around 20 UTC +- some hours.
But I think the "tradition" itself should be moved to not be in the middle of June in the future.