It's generally put down to the time needed to break in the Teflon caps.
I've had a Ref 2 phono SE for four years now and still only up to 391 hours ... and I'm not sure I can tell you if it's changing as over this long a timeframe lots of other things change as well. Put it this way if you don't like the sound of it at 200 hours (or for that matter at 20) it's not going to sound that different at 600
I've had a Ref 2 phono SE for four years now and still only up to 391 hours ... and I'm not sure I can tell you if it's changing as over this long a timeframe lots of other things change as well. Put it this way if you don't like the sound of it at 200 hours (or for that matter at 20) it's not going to sound that different at 600