It is not uncommon to have to time a sound cue so that a specific point in it occurs as a specific point in the dialogue or action. This means timing the dialogue/action from the point in the script at which the track has to start and then setting the start point for the track. It would be great if it were possible to play the track backwards from the desired end point whilst the dialogue/action was being run (in rehearsal, of course) - then all that is needed is to stop the reverse play when the desired end point in the script is reached, and voila! you have the start point for the cue.
Thanks,
Dave