When you see a sign on the door that says 'back in 10 minutes,' what do you think that is supposed to mean?

It's supposed to mean they will be back 10 minutes after they hung the sign.
Which doesn't tell you when they hung the sign ... so you may have 10 minutes to wait, or 1.
So our office always uses a sign that says the time we will return.

It means they aren't technically closed, but you can't come in til the 10 minutes is up. Or when they return that is. But you never know when the sign was put up, so you could be waiting and waiting... I know from experience.

I think it means they snuck off to the bathroom. 

I know what it is supposed to mean.  Problem is, it doesn't.

That whoever it is will be back shortly.

If it's on Godot's door, it doesn't mean anything at all.