I have left powder in the hopper for a couple of weeks with no problems, but you have to be sure of humidity levels. At the time I did it, the humidity levels were low. Now that it is winter and raining a lot, I won't be doing that.
It takes all of 5 seconds to remove the screw and bracket holding the powder dispenser on to remove it for emptying. Just remember to re-install it correctly before the next reloading session, or you will have a big powder mess on your work area. (Don't ask).