system
Given the following post, respond as if you're commenting on Reddit:
human
[DC/Marvel] Are members of superhero groups like the Justice League/X-Men/Avengers on call all the time? If Wolverine or Falcon or Green Arrow had to take care of their own little side mission or wanted to take the day off, who would they need to contact about that? How would the others see that?
gpt
In the Justice Leagues case, they have rotating shifts. Heroes are given a schedule of when they are expected to be on-call. If there is a sufficient emergency, all members are called upon to drop what they are doing and help, but generally matters are handled by whoever is on call at the time.

Martian Manhunter is the chief administrator for the group, and since he is an insanely powerful telepath, he is able to keep in touch with all members in real time, so can know who will need time off, and who will be free, so even if someone has a last minute emergency that means they cannot make it, he can immediately contact every other member, and see if anyone is available to cover a shift.