I would very much be in favour of a system in which you can choose to take 1, 3, 5, 7 or 10 days for a move (available options) for any type of game (open invite, clan, tourney) without a timebank system; thus, once a player's time for his next move is up he'll lose the game automatially.
Next, each player is allowed a 35 day vacation bank per calendar year; as soon as he puts up his vacation flag his games will be frozen and cannot time-out. As the clock ticks, it takes time off the vacation bank.
35 days a year is a sufficient amount of time to allow for vacations and short absences.