The "first time" charge shouldn't take any longer than any other charge. In my experience, charging a ST with an ST charger takes almost exactly 2 hours, from say about 30% to full.
So, the question is whether the Nook Classic charger is the same as an ST charger. Unfortunately, I sold my Classic, so I cannot answer that. Maybe you could search on this forum or via a Google search to find out. Or maybe someone will chime in here, hopefully.
If the classic and ST charger are the same, I'd say you have a faulty ST. It shouldn't be taking that long. Of course, perhaps you have a faulty charger.
You could try charging it via USB connected to a computer. If I remember correctly, that is supposed to take about 5 hours from low up to 100%. You can tether it, which will cause the computer to recognize it as a device, and then on the computer "detach" it (BUT LEAVE IT PHYSICALLY CONNECTED). In this way, you won't have it still active as a device on your computer system but it will continue to charge, and the green light comes on when it is full. It will even go to sleep while it is charging, as it does with the charger, which is fine.