In the lip area I recommend a hyaluronic acid filler such as Juvederm or Belotero. The results from these fillers are immediate (i.e. what you see is what you get), but there will be some swelling afterward which can take a few days to go down. In addition, the lip area especially is prone to bruising after injection, and these bruises can take over a week to fade. Your doctor may be able to laser the bruises to help them fade more quickly (our office offers this service complimentary to all of our filler and Botox patients), but you should still expect some bruising for several days. Also keep in mind that most doctors will error on the side of under correction, because it is much, much easier to add filler than to try and remove it. If you do opt for a touch-up, you can expect swelling and bruising after the touch-up treatment as well. Both Juvederm and Belotero last around 6-9 months.
Based on all the above information, I advise my patients to have filler in the 2 week to 3 month range prior to a special event. This way you have plenty of time to have a touch-up and let any bruising or swelling fade, but your results are still maximized at the time of the event.