I now work for a LE agency that has its own internal computer forensics lab. I'd be glad to ask any questions you may have (I can't answer, as it's all basically like Greek to me).
Watching those that do the forensics exams, it appears that they average 1-3 days to complete, but as you mentioned, there's usually a backlog. We did have another agency call one day to see if one of our experts could do an exam on a computer from a murdered man's house, and that one did get "bumped" up in the order. However, it was a new case, versus one that was 2 years old.