16:8 is already a start (in principle only omit breakfast or dinner, many already do this unconsciously), but to utilize the real benefits of autophagy, i.e. cell renewal and breakdown/recycling of both broken cells and waste products, the time window without fresh energy/calories must be longer. After 16-20h the hormonal effects only begin. For example, increased output of HGH, Human Growth Hormone (no, you do not grow, but the breakdown of muscle mass is prevented to a certain extent) or the adrenaline output.

These are evolutionary processes, people 10,000s of years ago often had periods where there was nothing to hardly anything to eat for days. The body has reacted to it, cleaned itself, the glucose in the musculature, body fat pulled up and at the same time hormones released which protect against tiredness etc., so that the body became more awake, more efficient for hunt and calorie procurement.

Until the glucose and the contents of the digestion are digested, however, it takes a certain time. 16 hours is not ideal, so I would try a whole day.

Of course, hormonal adjustments to fasting do not last forever. At some point, the chemistry and physics sets in and after a certain time without calories the organism dies (keyword: entropy). But that's several days/weeks without food.

Fasting or OMAD for one day is great, it has so many benefits. Not to mention how much time you save by not having to constantly prepare meals or worry about what to eat again.