You don't get nearly as much as you think you should mining under and around the rock. The copper nodes extend a significant distance into the ground, so mining just the exposed rock typically gives you around 50% of the total, and goes much faster than mining under and around the rock.

My suggestion is to find a place that 3-4 copper rocks nearby, ideally within visual distance. Make a temporary camp and so that you can refine and process at least most of it there so you don't have to haul it. Then just go out and mine all the exposed copper rock.

One more tip: Mining rock goes faster if you're standing on it, so do that if and where you can. You should notice that you have to hit the rock less if you're standing on it.

How long does it take you to mine the exposed portion of a rock? I can do it in about 1/2 day. It shouldn't take you longer than a day if you just concentrate on pounding the rock and not worry about moving the rocks around, etc. When you're finished it doesn't take long to sweep everything up and throw it into a chest / rock piles / haul it to your camp.