8-10 minutes should be expected... except, as indicated by the folks here, when a CDG disc is very warped (Chartbusters are the worst), or very scratched, the the drive itself will do multiple retries to get a good import. I have heard Sound Choice discs taking up to 25 minutes PER TRACK!
As requested by a number, tell us:
1. Roughly how many discs you have seen take 1-1.5 hours,
2. What are the Brand names and Disc numbers, and
3. What condition are each in (look at them on edge to see warpage, look down on them to see scratches).
Then, we have an idea what you are dealing with.