Day and night shifts draw from different pools. The number of customers the strip bar brings in increases with the number of girls you have working there. I'm not sure about the gambling hall, as girls don't get paid for working there, so I never put them on duty there.
My understanding is that you get something like (random base number of customers * advertising bonus + bonus from strip bar + bonus from gambling hall), though advertising could be additive instead of multiplicative. You have at least 3 random variables in the equation, though (as the customers you draw from the strip bar and gambling hall is based on the random number of customers drawn to those establishments in the first place [and the number of girls you have working in them, too]).