My quick answer is:
There's nothing to prevent you from trying to do this as a player.
However, since the 5 minute workday is no longer hard-wired into the rules, the DM is no longer obliged to design his adventures around it, or risk a TPK.
Since your characters are still fighting fit after using their dailies, just not quite as fighting fit, the DM is free to make a situation where you have to complete your goal in 7 hours, or fail. Sure, you can sit down and rest til tomorrow morning, but the princess is going to be sacrificed at midnight, and the legion of devils will be loose in the world, since nobody interrupted the summoning ritual. Or have buddies of the monsters you just killed show up and have at you while you're trying to rest.
Doing either of those things previously would be a no-no because in the first example, you'd be either forcing the players to give up and fail, or forcing them to commit "PC suicide" by charging in to stop the ritual when they'd be certain to die and fail anyway. In the second example, you'd just be arbitrarily killed.
Now, the DM can throw more time pressure and more adversaries at you without guaranteeing a TPK. So while you can try to operate under a 5 minute workday, the DM is no longer mechanically obliged to comply.
IMO, of course.