I tried it... Well, the developers don't seem to sleep on the moon.
As soon as I put the clock back to normal the following has happened: all my perfumes (2 counters, 6000 perfumes!!!) including the whole "1" floor was sold out. Floor 0 was almost like before, but there were some items sold. PLUS: I got a warning like "I'M VERY DISAPPOINTED YOU CHANGED THE CLOCK ON YOUR DEVICE. PLEASE BE CAREFUL. YOU CAN LOSE YOUR SHOP!"

PEOPLE, DON'T DO THAT!!

This one DOESN'T work for FASHION STORY because the game is a "live" game (Internet connection needed!). Progess is saved by their servers.
I haven't yet tried it in Fashion Story World. But I think it COULD work for a game like this where the progress is only saved to your device.