The rule is basically that whoever joins the game doesn't play right away
if going first. as a rule, players have to wait 12 hours before taking turn
if going first. that allows every player in the game to see the drop, make
the game more even and interesting to play.
this rule allows people to take the invites without worrying if they'll see
the drop. also, this rule avoids the problem of too many people waiting
to join the game and then missing invites in the process. if FoW is in effect
people have no reason to wait on joining the games.
usually, if someone violates the rule he/she
is obligated to reveal the play (copy/paste their game log).