3 days and a lot of Bawls.
As Far as the main topic here goes:
I think that it was Plaegus who willed the midichlorians to create a child who would one day bring "balance to the force." Thus meaning, if there can only be 2 sith, there will only be 2 jedi. Majority-wise, this happens. Many would argue that some other Jedi escaped, but who says there weren't other sith in hiding, not wanting to expose themselves for no reason. With one powerful Sith as Emperor, there would be no power gain for them to come out of hiding. Thus, the balance was maintained and that's how it went.