When the update requires downtime (or has such a high likelihood of downtime) that you'd be knowingly (or almost knowingly) inconveniencing users, do it off-hours (e.g. nights and weekends) and gather availability commitments from all the people you anticipate might be useful. If something goes so terribly sideways that it takes a long while to stabilize given the skeleton crew, at least you have plenty of time before users need it again. Friday evening maximizes that window.

Else, do it during regular business hours and very far from time off (whether that's CoB, weekend, PTO, etc. -- "not on Friday"). If something goes so terribly sideways that users are impacted, at least you have nearly everyone available so hopefully it won't take long to stabilize.

> Friday evening maximizes that window.

For the FAA it sure as fuck doesn’t.