How long is possible to last?

Use this method. It works 100%.

Whenever you have strong urges, tell your seeking dopamine brain that greater pleasure is better than pleasure. What's better than pleasure? Greater pleasure. A strong urge comes? Think about how big your libido will be in 3 months. Just that, when an urge comes, you only have to think about how big your sexual energy was when you discovered porn. Wouldn't you want to experience such pleasure again? Then wait 3 months and then decide wether to release the sexual energy and enjoy maximum pleasure.
The thing is that when the 3 months come, you'll most likely have forgotten about porn altogether or even if you relapse, your 3 months progress are not gone so repeat all of that for 3 months again until eventually porn is out of your mind.