The rule is “No change Fridays”

Absolutely. Just yesterday I had a call with cow-orkers, we have an problem on the environment which is actually quite a big deal and we tried to find a solution. Turns out we need to do a major version upgrade on one of our systems in the pile. But as nothing was literally on fire it's a problem which can wait until monday. There's not many cases in our environment which says it's mandatory to do any changes at friday/over the weekend.