SLA's for Response times

Hi All, I have currently setup our SLA's for ticket closure and was hoping the community could help me configure some SLA's to manage ticket response times. We would like to set SLA's/Timers for tickets that are left in the "New" Status, these targets would then be met and ignored as soon as the Status is changed to any of our other available ones. The time frame will need to be different depending on which Priority is set to each ticket. How would be best to configure this? Many Thanks, Mathew R