The current NICE (NICCE?) clinical guidelines state that post-CS, if all is well, and the mum is not feverish, you should be let out after 24 hours.
With DS1, I had an elective CS, it happened Wednesday noon, I was out Friday afternoon. But I signed myself, and DS1 out, against medical advice.
With DS2, I had an "emergency" CS (nowhere near crash), early in the morning on a Friday, and we were out on Saturday afternoon, without any stressful signing-out procedure.
One night is necessary, as you'll still have the catheter in then. After that, it depends on how things went, or are going.
Toothyboy is right about the whole counting days thing - if your CS is before noon, that counts as a different day. So if you want to spend a minimum amount of time in hospital, make sure your CS happens before noon. Hospitals are weird.