At 4 weeks of flowering I went down to check my plants and the lights were off due to my ballast failing by the time I got the lights back up and running they were out for 30 hrs. It's now a little over a week since then and alls good, although the time my lights come on and go off has screwed me up a bit and thrown my routine off. I don't think it hurt them at all.
The lights going out for a few hours won't cause any issues. If you are in vegetative mode and the lights go out for a few days, it could trigger flowering, but it won't hurt the plant if it is already flowering. If you have extra dark photoperiods, the plant might stretch a little, especially if in veg mode, but if it is only for a day or less, I don't think you will have any problems.
You are safe, up to 4 days then issues start. Biggest would be air circulation and mold issues so open tent and allow natural convection . And close up at 12 hr Mark. Otherwise it would be fine. Don’t feed or water as they won’t uptake anything lights out