Your SLA changes with your priority. Which, not really. You have three SLAs. 4 hour response, 1 hour response, and 1 hour 24/7.
Priority can adjust between tickets and during tickets to sort according to which needs more immediate attention. Once the immediacy of the ticket is addressed, you can reduce priority while maintaining your SLA for that ticket. In this way, a high priority ticket can be acknowledged, triaged, and potentially reduced in priority if a bandage/workaround has been applied. The SLA stays. It needs to remain constant throughout the ticket.