There’s another team in the opposite timezone that handles on-call, for the majority of Google SRE teams.
Additionally as noted elsewhere, on-call time is directly compensated.
With a 5 minute response time service: you are credited 2/3rds of the hours that you are on-call outside of local business hours. These can be used as additional paid time off, or paid out in cash.
With a 30 minute response time service the hours are credited as above, at 1/3rd time.
One big benefit of directly compensated on-call time is it removes much of the difficulty of covering shifts.
Instead of everyone feeling like they have to keep track of who owes each other a shift covered, it’s just paid out. In vacation hours or cash. So if you pick it up, no stress, you’ve been paid for it.
Additionally as noted elsewhere, on-call time is directly compensated.
With a 5 minute response time service: you are credited 2/3rds of the hours that you are on-call outside of local business hours. These can be used as additional paid time off, or paid out in cash.
With a 30 minute response time service the hours are credited as above, at 1/3rd time.