Turning off my light

My plants are a couple of weeks old and I'm still in the veg stage. I have been giving them darkness in the evening for about 4 to 5 hours per day (6:30pm - 11:30pm). I want to gradually work towards the 12 hour dark period. Here is my problem. For security reasons, I will have to turn off the light on Sunday for most of the afternoon. As soon as the security issues are resolved, I will immediately turn it on for it not to reach 12 hours of darkness. I'm also planning on not turning the light off the night before. It will only be for this one day. Do you see any negatives to doing this? Cause if there is, I can work around it but it will require some labor on my end. I'm thinking that this will not be a problem, but I would like your feedback. Thanks

if its just for one day, a longer period of darkness will be fine i think.
the plant needs consistent 12 hour days for the chemical changes in flowering to start working properly, unless the plant is quite a bit more mature than yours.

It shouldnt make much differnce if its only for 1 day, but its not a good idea to do it more than that, because once the plant is in the 12/12 light schedule the plant measures the 12 hours of darkness and that is what releases a fllowering hormone.

One day should be no prob at all. But definitely don't go beyond that, or you'll be accepting serious risk of some hermies.