If you're a distributed remote company with people who prefer to work early and others who like to work late, all in different time zones, what are "normal work

If you're a distributed remote company with people who prefer to work early and others who like to work late, all in different time zones, what are "normal work hours?" Also, I work I higher education, where things move slowly. Although we don't have an assumption that after-hours emails will be replied to until the next business day, any delay of a day or more can cascade to far more delay on the other end(s).