Answer
About 1 minutes. In review, anything from 0.667 to 1.5 counts as right.
The worked estimate
7 × 24 × 60 = 10,080 minutes. 0.01% of that is 10,080 × 0.0001 ≈ 1 minute. A single failover that takes longer breaks the SLO, so four nines needs automatic recovery, not a person paged to fix it.
Numbers: Numbers to know.