What style of beer is it?
2 weeks is a good minimum..it depends on the style. I let my IPAs sit for 2 weeks and then refrigerate and drink. They're typically better after the 3rd week. Hoppy beers are best fresh, as the hop flavor and aroma can be greatly depleted after sitting for too long.
Other types of beers can sit for longer in bottles. Big beers, like imperial stouts and barleywines, can sit for weeks or months and typically mellow out and get better with some age. Properly brewed barleywines can sit for years in bottles.