Last time I heard mollies talked about for cycling a SW tank was 88'. Must be an old timer suggested that.
They live in brackish waters but don't thrive in full salt. However, since they are easier to catch than damsels when they complete their task and cheaper its more convenient to sacrifice them. Would have been a lot faster, cheaper and less cruel to simply use ammonia.
If your intent is not to keep them after the cycle just return them now. Toss a 1/4 teaspoon of ammonia in the tank and if the LR is actually LR and livexsand actually live sand it will be neutralized in a day.