YMMV, but when we do it, we'll actually wait until primary is nearly finished before dry hopping. If you move to secondary, you could actually pull it off the yeast cake for re-use without getting a ton of hops stuck in your yeast.
4-7 days is good at the end of primary/beginning of secondary should get you want you're after. If you're looking for a HUGE punch of aroma, then 3-4 oz (in 5 g). A regular nice nose is what you'll generally see for 1-2 oz/5g.
Vinnie Cilurzo from Russian River actually recommends two different dry hopping periods for an IIPA (once early and once late), but for a single, one 4-7 day period should do it.
Drinking it fresh will be better than waiting.