If you're running forward-facing sonar and know how to read the graph, it's a pretty well-guaranteed fish and doesn't take long. For the more traditional methods (graphing at the console and trolling around), I'd say 1/2-2 fish per hour is "average". A lot of it depends if the fish are schooled up or scattered. The more schooled up they are, the easier it is to hit them.
For example on opening day this year, we graphed and snagged the usual way for a few hours and caught four fish. That's about average for us. We ended up talking to another angler who had Livescope on his boat and asked if we could hop in and try to snag a few spoonbill. In less than 20 minutes out of the same hole we'd been blind casting, I boated an 82 and a 65 pounder. Livescoping paddlefish is stupidly easy.