I agree with Gary. With 7 hours to go, some over-the-counter nasal spray, oral antihistamine, or oral decongestant is about the best you have. Warm water with salt gargles, tea with lemon, tylenol or motrin, and similar suggestions may also help.
If there was more time ...
There is some evidence that suggests that zinc and vitamin C, if started at the first signs of a cold, can shorten its course.
A steroid nasal spray (prescription needed), and can also help with sinus symptoms from colds and allergies, but usually takes a couple days to kick it.