How long it takes to get back to normal after an episode of acute kidney failure?

Depends: If you have a less severe form of acute renal failure (ARF) like dehydration then probably a couple of days. However if you have a more severe form of ARF like a glomerulonephritis or infection causing acute tubular necrosis, the your recovering time might take weeks. In the severe form, you also may never get back to normal kidney function as well.