10 minutes to alert, to avoid flapping false positives. 10 minute response window for first responders. Or, 5 minute window before failing over to backup alerts, and 4 minutes to wake up, have coffee, and open the appropriate windows.
That’s some very carefully chosen phrasing.
I think if you really wanted to do on call right to avoid gaps you’d want no more than 6 hours on primary per day per shift, and you want six, not four, shifts per day. So you’re only alone for four hours in the middle of your shift and have plenty of time to hand off.
I'd like to think that a company the size of Microsoft can afford to have incident response teams in enough time zones to cover basic operations without relying on night shifts.