I guess it depends on the amount of fat but yeah if you push too hard exercising while carrying a lot of extra pounds you risk injury.

You can exercise for a full hour hard as you can, and burn the same amount of calories that can be eaten in a few seconds. I've seen people go workout then think it gives them an excuse to eat more. Been guilty of it myself to be honest. Like that old maxim you can't outrun a bad diet.

I suggest reading a book by an actual sleep scientist instead of relying on reddit armchair specialists.

I recommend "why we sleep" by Mathew Walker. He breaks down a lot of the research on sleep, a lot of it was surprising in that, even in the last decade they have learned a lot more about what is going on in the brain during sleep than I expected. I assumed it was still mostly a mystery.

But if I had to give an answer to your specific question I would guess if the new planets rotation was close enough, we would adapt to it but 48 hours would be too long. There are waste products that build up in your brain just from the activities of sleeping, and when you sleep cerebral spinal fluid is pumped through your brain to flush them out. Glial cells even shrink a bit to facilitate this process. That's happening in deep sleep in other stages memories are being shuffled from short term to long term memory, in rem there is a lot of dreaming, they speculate its purpose is emotional stability, There's a lot going on but ask yourself how you feel after being awake for 48 hours.