Nemesis Destiny
Adventurer
Here's how I'd do it: the players don't get to say when they take an extended rest - you do.
They can take as many short rests as they can squeeze in, but sooner or later, they'll run out of surges and spent daily powers are gone until they come back. In my game, I let players recharge daily powers by spending lots of healing surges to do so, and I don't give them auto-healing after a night's rest.
So extended rests happen at key spots in the story arc. It says they must be at least 12 hours apart, minimum, but nothing says an extended rest has to be available every day. Like most terms in 4e, "daily" can mean just what it says, or it can mean, "it comes back when it's good and ready."
They can take as many short rests as they can squeeze in, but sooner or later, they'll run out of surges and spent daily powers are gone until they come back. In my game, I let players recharge daily powers by spending lots of healing surges to do so, and I don't give them auto-healing after a night's rest.
So extended rests happen at key spots in the story arc. It says they must be at least 12 hours apart, minimum, but nothing says an extended rest has to be available every day. Like most terms in 4e, "daily" can mean just what it says, or it can mean, "it comes back when it's good and ready."