Which period in a 24-hour cycle does the human body burn the most amount of fat regardless of what physical activity it is doing?

Wouldn’t that depend a lot on the specific human body in question?

Morning.
Working out in the morning — especially on an empty stomach — is the best way to burn stored fat, making it ideal for weight loss.

From what I understand the digestive system is busiest during (the) night/sleep.
Don’t know if that automatically means that burning of fat happens then too, but I would bet it did.

Of course you’re going to burn the most calories when you’re the most active. Clearly, you cannot apply a specific time of day or night as a universal dictum applicable to all. A night watchman who sleeps through the daylight hours of course will expend more energy in the dark than the office worker snoozing away.

Resting metabolic rate does vary through the day: https://www.cell.com/current-biology/fulltext/S0960-9822(18)31334-4

However, this isn’t “burning fat”. Burning fat basically requires a sustained caloric deficit over a number of weeks or months. The general recommendation is a deficit of 500 calories per day.

The hard part is calculating intake and expenditure, and sticking to a course of a modest calorie restriction.

There’s no special time of day for more fat burning.

I don’t know but was surprised to read how many calories are burned during sleep.