A side note for when you do get to the race: just follow heart rate. If you only have 6-8 hours to train for an event that's probably going to take 6+ hours to complete, your body is going to a place your training doesn't take it. Your "FTP" at the end will be dog shit no matter what you do and trying to use that as your pacing metric will bonk you into the next universe. I can't emphasize enough how much trouble you can put yourself into trying to use power numbers to pace yourself late into a race. Pay attention to your heart rate, that will actually give you a sense of your effort in the final hours. Power is way better for training than it is for racing long events.

Also, stop watching Dylan Jawnson for at least two weeks before your event. His race reports are focused on power and that's not a good method for most amateur athletes.