When I was briefly working in a construction plant. Weekends is when non critical or potentially risky operations on machinery would be done, as to not block the production chain during workdays.
I've yet to see the place that had the level of testing, and infallability of the CI process, to where I wanted to deploy on a Friday. Yeah, it may be a low chance that anything will go wrong, and an equally low chance we'll be unable to easily rollback, but so few things can't wait until Monday that I want to roll those dice.