@13 - That would be interesting. Having a 2 hour promotion, but have it begin upon login, and it can only start within a 24 hour frame.
For example: Promotion will only be available on Saturday. It starts upon login, and login must be on Saturday; however, after logging-in it is available for 2 hours (so it may run into Sunday morning). If you do not log in on Saturday, the promotion will not be available for you.
The coding aspect is a bit of a nightmare; however, you could probably steal some of the code for the Christmas/Monthly stuff (Daily Login) and combine it with the current Promotion stuff. You might have to even tie the promos to the in-game shop, instead of the web's shop. Tying it to the day would also prevent rampant abuse from potential multi accounts, too.
Just a random thought. =P