In general, I would say that convention events running late is a management failure, not a technical one. (This discounts acts of Ghod and truly unforeseeable developments.)
In my years of convention attendance (going back to 1984), I've encountered an attitude that "of course, all Events start late." When the 2005 Worldcon in Glasgow asked me to manage their Events division, I decided to make starting on time a priority, and every one of the area heads knew that, and all of the staff under them knew that. It was not easy, but we did it. The latest start was 1 minute late, and that was partially because we actually forgot to include in our timeline a single person who could say "go," which left me — because I was actually the first speaker on the event in question — running around at about curtain -10 minutes trying to figure out who would give me a cue. (We fixed this before the next night's event.) We also had a Sword of Damocles hanging over our heads to not run long, because on the final night, we had to be 100% out of the building by midnight or face a large (high four figures in GBP) half-day rental on the event center. We did it, and I was happy to approve the expense voucher for drinks and food for the events crew who made it happen, but as far as I could see, nobody was killing themselves trying to make it happen. Working hard, yes, but not destroying themselves.
Our doors opened on time (and could have opened 30 minutes early, but the paid stewards wouldn't open them). Our events started on time. I'm pretty sure we had some people turning up at 8:45 for the 8 PM masquerade saying, "What do you mean, it's already running? These things always start an hour late." (In railroading, the equivalent is "How dare you actually have the 5:12 PM departure actually leave at 5:12!" which was said to be the reaction of commuters when the Rock Island cleaned up their act with their commuter trains and got them running on time.) Our events ended within the expected envelope, and we were out of our venues on time.
We managed to do this because everyone, at all levels, knew that it was a priority to get it done, and they worked to make it happen. The priorities were communicated through every level of the event as far as I could tell. (The staff did throw me out of backstage during rehearsals because as they put it in keeping with the convention's "Spaceport Glasgow" theme, having the Captain prowling around belowdecks was making the ratings nervous. They were right to do so.) I'm proud of the job we did in Glasgow, and I am happy to point to it as an example that says, "We can do this."
Events is not my responsibility at this Worldcon. I'm merely a staff member over in the Business Meeting. But I'm saying here that it is possible to make things run to time, as long as everyone involved, including the event participants, commit to doing so. If you assume that things are going to run overtime, they will run overtime.