Usually the offer is rolled out within a few days. It may take up a week or so.
I got the offer letter on the same day of interview.
Actually when I was called from Citiustech, it was a walking drive for 50-70 candidates. There were 3 rounds, 1st purely technical, 2nd technical+managerial and 3rd is HR. So if you can clear 2nd round with manager then you are 80-90% onboarded.