It always amazes me why someone would want to go down the route of having mollies in a marine tank, when we have the vast array of colorfull saltwater fish....amazing.....
Most of the people I've known to put mollies into a sw tank do so for algae control. This is especially true in tanks that are too small for a tang, or in tanks where the person didn't want a tang for whatever reason. Others have acclimated mollies to sw to use as food for their predacious fish (lions and anglers). Here's an online article that talks about it a little, and states it really doesn't require days or weeks worth of acclimation to move mollies to sw.