You need some successes to build upon. If your current goals are two hours too long, try making them an hour and 45 minutes shorter. Then when you’re about to cave, you can remember that it’s only another 15 minutes. And surely you can hang in there for fifteen more minutes, right? Just distract yourself with something shiny and when you look up, hooray, you’ve met your goal! It doesn’t matter that it’s a littler goal than you first aimed for, because it was challenging for you where you’re currently at, and you did it. Once that’s easy, then you can start increasing it again. With a good solid foundation, you can actually progress relatively quickly to longer fasts, you just need to build up the skills in the first place.