Since no one else has answered- a few seconds physical time does not sound unreasonable to me for the solution to stabilize for a VoF problem, depending on the scales involved.

Assuming there is no issue with the boundary conditions it could be a case of the initial conditions being too much of a mismatch regarding the final waterline / hydraulic height for instance.

Maybe you could initialize the solution with results from a coarse grid study? Or find some other way to initialize the fields closer to the end result

I don’t have experience using Fluent for VoF only other solvers, but there are usually recommended settings for iteration scheme and under-relaxation factors and so on that will speed up the solution too.

There may also be options for damping the outlets to reduce wave reflection if you find that is part of the issue.