How long does a nose piercing hurt for?

A properly done nostril piercing should only be uncomfortable at the most for 24 hours. If the piercing is still uncomfortable past the 24 hour point then chances are good that there is some form of issue with the tightness of the jewellery in the piercing, cleaning procedure, method used to conduct the piercing.

If the piercing was done with a piercing gun, well then there's your problem. Piercing guns are never to be used to pierce anything other than ear lobes. In Canada "Health Canada" has made it more than clear to piercing gun manufacturers that they are not permitted to use piercing guns on anything other than ear lobes. This policy has also started to appear in most US state health guidelines for piercing services.

Now if the piercing was done by a professional body piercer, I would suggest you revisit your piercer and have them look at the piercing to ensure you have enough room on the jewellery piece for the possible swelling and cleaning requirements. The method used to clean the piercing could also be causing you some issue so this can be discussed with your piercer.