The more lean muscle mass the fighter has, the larger percentage of his body weight he'll be able to shed.

When it comes to cuts, some people prefer to do the largest portion of it on the day, others like to do the old school boxing style thing and cut it over the last week. There's no doubt that, coming from a purely biological perspective, the first method tends to be the safer and healthier method. It should also provide just as large a weight cut.

Typically speaking, the shorter the length of time you spend dehydrated the better. Unless you're travelling a great distance to make the weigh in there's really no reason to spend any more than an hour at min hydration before starting the process of rehydration.

Many fighters nowadays are moving away from the old school boxing stuff and like to switch diet to a pure protein diet about 2 weeks out from a fight. This strips the last kilo or two of fat from the body and maximises lean muscle mass when coupled with the last two weeks training. This also, in turn allows for a larger water cut. Many will simply drop down to a half litre of water per day for the last 2 days and do most of the water cut in the sauna immediately before the weigh in. An extra part many do is "water loading" which is, a week before the weigh in, to drink about 6 litres of water a day then do the cut down to half a litre a day 2 days before the weigh in.

That, of course, is an ideal situation, it's obviously different when you're travelling to the weigh in etc.

When I was coaching in germany, my first fighter who was, to be fair, completely ripped, managed to drop about 5.5kg in water quite comfortably over the last day. This was for a 68kg fight (i think) lol.