I feel like many or most places already have the "be cool late Friday" mindset. Emergencies or critical things can still happen, but if possible maybe don't schedule a long meeting end of day Friday. Don't ask for something that needs turn around after the morning as people already are going to likely be in a wrap-up mode. It always feels like a very implicit "can this wait till Monday?" attitude permeates the day. And it's not just being nice, splitting a task over a weekend can lead to things being forgotten or missed or just the context being lost. Hell, I've seen places operate more in a "be cool all of Friday, it's the pseudo-weekend".

All that is a long way of saying that that group feeling now exists a whole day before and it's important to communicate that.