b&r - your SLA will depend on the tape SLA to get data from tape. I'd set this at some xx minutes per GB. Test in your environment.
User Access - ? not sure what you mean
Purge and Archive - Is this time to perform purges?
Usually we have response times for on call / critical issues set to 15 minutes. Resolutions have been SLA's anywhere from 2 hours (depending on issue) to 6 hours.