a requirement of champs "rules"?
Definitely not. That would be insane.
What - a fish warning too?
Probably not but typically any non-champs riders might get sent off after the "official" riders for whatever reason, not that it makes a difference to people out on course (especially not in MTBO where I generally have no clue who is on what course).
It's the same for the long champs - 52 entries spread out between 10:15 to 11:18 with no two starters on the same minute. Even the nationals had five starters each minute (although there were 2-3 minute gaps between each group). I don't know which method I'd prefer either as a competitor or an organiser!
Actually that's not entirely correct - there are a couple of early categories (M21 and W60; M50 and W70/W80) that do start together.