most airlines do have company limits, but there is no FAR giving a max limit.

as my check airman told my on my line check to finish IOE at TSA (which i did in 39.9hrs) that most people are usually let go if they don't finish in 40hrs because it could be a liability to the company later if said pilot goes off the end of the runway at a later date.

it takes as long as it takes, but hopefully not so long that you miss out on a few bid periods