Warm-up time.

It takes my system about 30-45 minutes before it 'gets going'.  I wonder, though, if just leaving the system powered on does the trick, or if you actually have to be sending signal through for it to make a difference.

I have the same question as parabolic.
The only things I keep powered up are my SS phono-pres.
On some sessions I think I hear an improvement after 20 minutes, on some I notice no change. The ones where I do notice a change are usually playing LPs vs digital sources. And usually with a DL-301 vs a Shure V15.

In my experience it’s 20 minutes of actual playing time for a solid state amp.  So I throw on a CD, leave the room/go about my bidness and when I return the system is ready to pay some sweet sonic dividends.

Contrary to some of what has been said, tube electronics warm up relatively quickly.  CJ and AR both suggest about 30 minutes.  SS stuff can take hours.  The advice to leave SS stuff on all the time, especially if it is not Class A, makes a whole lot of sense.

Perhaps being on your second or third drink is making that "warm up" sound so sweet!