Something is not right with the freeze time; or at least it does not work as I guessed above in the second post.
Yesterday evening, we started a normal-turn 2vs2 to welcome a new player, non-ladder. All four of us were online at the same time (and would be for another hour), but when my team finished its turn, we got 6 hour freeze time. However, within the other team, one player could play their 2nd turn immediately, while the other player had to wait only 4 hours, but not 6.
EDIT: We don't recall the order in which we ended our turns, but I believe the player being allowed to play the second turn right away ended last.
This seems quite buggy to me. Maybe it is due to not being in ladder mode?
EDIT-PS: Yes, a real-time game might have been the better choice, but I was on the train with an unreliable connection, so that seemed risky.