Rolling 120h with 48h water for 21 days total is quite a long and demanding period.
Do you have a good fasting workout?
Regarding the refeed period, the theory says that it should last at least twice as long as the fast itself.
my 2 cents: If the goal is weight loss, based on when you want to reach your desired weight, you would probably get the same effect by inserting a few days of refeed between one fasting period (DF + WF) and the next.
People frequently quote 2x the length of fast, so 42 days for you. According to that.
If you did a solid water fast for 21d you would be guaranteed a steady 10kg loss in fat. And it’s very ‘doable’ 21d dry / wet is going to be a B*
Can I ask how much you’re planning to lose and how much you weigh?