The only point that I won't to make it our work is not independent of the work the actor/director does, and any director who allows the tech to go determinately behind schedule is not really doing their job. As a SM, we need to have an ear on these conversations and be able to make the snap judgment - is this a conversation that just start to fill the time while the sound deisgner took time to rewrite the cue? is this a conversation that is going to wrap up when I announce we are ready to take it back? or is this a conversation that is going to go on for a bit? At that point, I need to make a decision - does this conversation need to go on? or should I get us to move on?
But, since you are dealing with students, and some who have never been through the tech process, talking to the director and designer and fleshing out your concerns about time, and giving your expectations for each tech period and see if you can get everyone on the same page with you. (I do a lot, by end of day 1, I want to be at intermission, by end of day 2 I want to the get through all the fights in act 2 and everything but the last 3 scenes, by the end of day three, I wanted to finish the show, and then go back and work the dances, etc, etc, etc.) If you take the time to spell out everything with your director and design team, before you get to tech, then they may be more open to you rushing them in tech. (I HATE, HATE, HATE, HATE comments form directors who feel like I am pushing them - the directing process, including tech, is not something a lot of directors can do just on command - it's about creation, problem solving, is balancing text versus stage picture, etc, etc, etc). Often, during this pre-tech conversation, there will say, I want to do three runs before we open, at that point, I would say, if we want three runs . . . then we need to finish q-2-q in 8 hours. At that point, we have already laid the ground to your cracking the whip at keeping to schedule. And if you find yourself being bogged down by conversations, you can pull the director aside and say "If we continue at this pace, we are not going to get to three runs through you wanted." At which point, they may turn to you and say then I will only do two runs.
Again, if there are major issues to deal with acting-wise, then what is the point in having an additional run-thru of a play that is bad?