Ah, excuse my stupidity, now I see both why it makes sense to allow both to play at once and why the hand order can't be changed then. (In the move order that I suggested, your button hands could be played in any order as the opponent would see neither of them until you finished all the 10.)
When the duel starts, you begin with hand 1 and the opponent - with hand 11 (I'm not sure if it's displayed as hand 1 or hand 11 to him, but let's number the hands from your perspective). Then you both proceed to play hands in strict cyclical order - you play from hand 1 to hand 20 in ascending order, then hand 1 again right after hand 20, then from 2 to 20 again and so on; the opponent goes from 11 to 20, then from 1 to 20 in ascending order and so on.
So you never see any of the moves that the opponent made while you were thinking on your pending moves, until you clear that backlog.
All genius is simple
This move order resembles two trains on a circular railroad that start at its opposite points and can't pass each other. When the opponent's train bumps into yours, his clock stops ticking, and it restarts when your train moves again.
E.g. the game can proceed as follows:
You act in hands 1-10 and he acts in 11-20 at the same time. You can't see what's happening in 11-20 until you finish hand 10.
You act in hand 11 and close the app. He acts in hands 1-10 at the same time, only then he sees your move in 11 and replies there too and closes the app.
Now only your clock is ticking and you'll have to restart with hand 12, play in ascending order up to hand 20, then hands 1 to 11. The opponent will be notified as soon as you act in hand 12 and will have to start with it regardless of how many other hands you'll have acted in by the time he reopens the app.
Right?
Then there's no sense in stalling indeed.
Last edited by coon74; 03-11-2016 at 10:12 PM.