How to make weekdays recurrence to work with different timezones?

[buxbunny110]

Server time is set at UTC by default, I have users who set the ads for certain country zones, for example if it should be for Hong Kong then it's +8, I have form where user can select days when the ad should be active, the problem is that Monday is not the same for everyone so I need some way to shift recurrence, somehow make recurring work with particular timezone, I thought just to have additional select box where user would select the timezone and then I could do something with that, the problem is the interface, I'm not sure how it can be done, kind regards.