I bought a peach "kit" at my LHS and, after a few tries, it is now
happly fermenting.

How long should I leave the peaches in the fermenting must? A week?
A few weeks? Until I rack into a secondary? Until I rack in a few
months after that?

I just stir and mush up the fruit a litte more every day to keep
things stirred up. It has reduced in volume by about half due to
juice being squeezed out or the fruit breaking down.

Thanks!

Alex.