Thought I'd quickly post back as I've had a bit of a discovery.
I used SD 6.3.1R1 to mount a snapshot from one of my T2 storage boxes and it was really quick - this is the first time I've carried out this activity. I made an assumption that SD 6.3.1R1 was the issue, but it looks like that isn't the case. When I solve the issue I'll update the post.
Re: Snapdrive 6.31R1 takes very long time to enumerate disks