I really wish that famous sims would not be included in the potential employee pool. I hired one and had to fire her because the place was swarming with paparazzi and no one was working because of this. I usually keep the stores open until the employees announce that it is time for them to leave and I think that depends on when the store was opened. I think you may be able to get an employee to come in later if you keep a hire slot open and hire an additional employee on the spot whenever you need him. I think it would be nice if the stores had separate open hours and working hours, so we could have say 6 hours for talking to customers and selling and 2 hours afterwards where employees could attend to restocking, cleaning and repairing.