I often plan my Frontier travel about 2 months ahead of time. That's when I generally know where I need to be, and start looking for their crazy cheap fare sales. There's one major problem with this strategy: what I book two or more months in advance is almost NEVER what I actually get to fly. About 90% of the time, my flight times change by more than a hour, and often by more than 6 hours. Obviously, this can often be super inconvenient. Frontier will generally only make it easy to rebook flights on the same day, but that often doesn't work. Like if you're booked to fly out at 9 am, you don't want to fly out at 9 pm. They don't automatically offer you the option to fly a day before or after: you have to endure the Chat feature if you want to switch days.

I assume this greatly annoys many travellers unfamiliar with Frontier's complete lack of interest in sticking to their existing schedule. You definitely don't want to book any firm plans based on your initially scheduled arrival time. I don't think I've had a material schedule change less than a few weeks out, but you can almost always be certain that your flight time will change if you book two months prior. It's annoying.