In support the key values are response time (until the first qualified answer) and resolution or restore time, tiered by priority. It matters whether the clock runs around the clock or only during business hours.
Availability figures sound alike but differ a lot: 99.9% per month allows about 43 minutes of downtime, 99.5% already about 3.6 hours. It also matters what counts as an outage and whether planned maintenance is excluded.
An SLA only helps if it is measured. Ticket systems should make the clock visible and warn early, so that escalation happens before the breach, not after.