Sorry, but no slack. As a paying customer, and a guy in the IT business for 27 years, I expect maintenance windows (potential outages) to occur during off hours, and I expect (of course hope against) only sev 1 or unplanned outages during normal hours.

That is just the way it is done, period.

There is insufficient amount of paper in the world to list the number of times when IT people go make a change that is not supposed to break anything, but does anyway. I even periodically do this wonderful practice myself! This is why, repeat after me, we never change production systems during normal operational hours.