I think this is still pretty much in the air. I read some studies and reviews about how intense exercise with surplus can lead to metabolic increase, but my understanding is that they are far from conclusive.
That said, if you are to follow this plan, I would reduce your calories in eating days by a lot, especially in the beginning. This is for two reasons: we constantly underestimate what we eat, even when we try to measure it all, and also the fact that the TDEE that you mentioned is an estimate, not something that necessarily applies to you as individual, nor something that is constant over time. So if you start with, let’s say 2200, and you lose weight in the first two weeks, you can move it up a bit. That’s better than starting with 3000 and actually gaining weight.
To see how easy it is to make mistakes with this calculations, a cliff bar has 250 kcal, it is very easy to let up an equivalent of that get through your measurements. Let’s say that 10% of error is reasonable on the estimate of your TDEE, so that it is 260 less than that. That adds up to around 500 kcal a day when eating, and 250 when not eating. Sum that up and your deficit disappears completely.
I’ve been doing a 48 hour fast once a week for several years now. As far as weight loss it has mainly just kept me from getting any fatter (50lbs overweight). I might have lost a few pounds but not a whole lot. My diet is terrible, fast food usually 1-2 times a week and not much better for the rest of the week - sandwiches or whatever I can slap together on the run.
What it’s really done for me is in my bloodwork: from prediabetic to normal and a horrible HDL/LDL ratio to normal, albeit high normal.
Fasting works differently.
When you do the traditional diet you are operating on a caloric deficiency. For the post part your body tries to use what comes in and begrudgingly burns fat as a last resort. It will go as far as lowering your metabolism and cannibalizing your lean muscle mass.
When you fast your body quite literally and pretty seamlessly switches to an alternate source of energy, body fat. The liver runs out of glucose and it starts processing fat into ketone bodies for fuel.
Say you fasted for a full 40 hours and plan on eating on the next 8 hour window. There is no deficit to make up; all your fueling is to support yourself moving forward. At this point you want to replenish nutrients not calories, but you want to eat enough to satiate you for the next 8 hours. Heck you don’t even need the full amount of calories that you would otherwise need for a full day. Once your 8 hours are over and you feel happily full, the cycle starts again.