In the military, we had a 2 hour recall for a large chunk of our battalion, about 200 people for a few months at a time. If you got a call, you were expected to be ready to go in less than 2 hours. Social norms meant the expectation was closer to 45 minutes than 2 hours.

I think oncall is a common requirement for anything involving large sums of money, treatment of high risk injuries, or geopolitical power struggles.