So... how did it work for Callahan?

One day he got up and he was in a world where the bedcover of the motel room where he stayed was pink (it was in Leabrook) and some days later he got up in another one where it was orange (in Fort Lee). So he could tell easily in which world he got up.
But hey... if he was slipping from one world to the other... doesn't it mean that once he existed in this one and on the other day he existed in that one?

It means that when he went to work to Leabrook Homestyle Dinner he didn't exist in Fort Lee so he could not go to work there!
Do you get the point?
He can't exist in two worlds at the same time so he must be missing in one of them and it means he should get fired very quickly because on every second or third day he doesn't go to work. (We know he does but in another world.)

Or can he exist and go to work in both of the worlds at the same time? How so? If he can't why doesn't he get fired very quickly? (I am sure you remember that the owner of the place told he if he was late twice he would get fired immedaitely.) How can he work this way for 3 weeks?
I hope you see where the hard paradox is and why I don't find the answer.
I hope you can help me.