I just installed NOS tubes?

You should hear a difference immediately. I use this tube too in my VK-30. (Amperex 7308 white and orange labels).

-Ed

I take it from the tone of your post that you are unhappy with the new tubes. It may be that you were sold tubes that are worn out or are fakes. Some people that claim to sell NOS(new old stock) are actually selling WOOF (worn out old fakes).

The other points above are valid. Let them cook for a while and see what happens. The designer of your amplifier may have chosen a particular brand of tube because it has some characteristic that works well in his design. For instance, maybe the originals are on the high end of some spec like input capacitance or gain and the NOS tubes are on the low end. These tubes would sound very different and the NOS might sound worse.

My experience with tubes isn't as extensive as other A'Goners, but I've noticed with both my Blue Circle BC21 and Kora Hermes that whenever I changed the stock tubes to NOS to varying degrees I could always hear an immediate difference.

Tubes don't seem to need as much time as other components to "break-in", and I've also noticed that some go through drastic character changes before finally settling in. In my limited experience, 48-96 hours sounds about right.

I purchased them from Upscale Audio for $65.00 each. Initially the sound was comparable to the stock tubes but in another 2 hours the sound began to change especially in the mid-range. More detail so far.

I use NOS in my CJ premier 14, I notice a change immediately when I switch out. I go back and forth between stock and NOS.