Many people snack right up until bedtime (sometimes even literally in bed) and then rush to feed again the second they wake up. So technically, there is a fast

Many people snack right up until bedtime (sometimes even literally in bed) and then rush to feed again the second they wake up. So technically, there is a fast during sleep, but technically, there is a fast every second you don't have food in your mouth, I suppose. The point is, duration is important. I don't know if there's a standard, but in the intermittent fasting literature, 18/6 is one of the common schedules, so you'd eat from noon to 6pm for example. The other 18 hours would be 0 calorie intake hours. Rather than fixed schedules, what you need is a period of time long enough that your body enters ketosis rather than using energy directly from glucose. The schedules are a rough guideline.