As you can probably tell from the silence, I think the answer is that out of the box RT just bases SLA progress on the ticket creation date.
You could change this with your own locally written SLA module, and this thread might be of some help. They were moving through SLAs by ticket status changes, but there is some information in there about changing from ticket creation date (in their case to the last status change transaction time).
If you’re not a coder, Best Practical do say in their blog post about SLA that they’re open to contracts to get it to handle specific use cases.