Tier 1
5 mins
24/7
Highest SLA - expectation is that an engineer is working on the problem within 5 minutes of a page going out.
Tier 2
30 mins
24/7
Moderate SLA - for services that can accept short-lived degradation / outage of service without impacting external customer SLAs.
Tier 3
1 day
Business Hours
Weakest SLA - for internal services that can tolerate degradation / outage of service for longer periods of time