Sometimes, a game is so epic that you agonize over every move, trying to think 5 turns ahead. Sometimes an opponent is so awesome, you spend too long chatting and not long enough playing. Plenty of other reasons that on occasion, the 20 minute net time limit per player is a BAD thing. Though most times it is great. Please add a "Request More Time" button that shows under the timer when you have less than 5 minutes available. If you click this, then your opponent is allowed to agree with the extension (via popup request). If they do, then both players gain an additional 5 minutes. If they do not agree, then the button is disabled for the remainder of the game (so you cannot spam them to annoy if they refuse), though the opponent will have an "Allow more time" button show for them under your clock (in case they change their mind).
I'd also love the option in casual MP games to set a different length timer (or even just turn the timer off). I don't particularly care for a game against my brother to be decided based on time.