Hey!
If you are talking about the amp than minimum of 50hrs, but 100hrs would be a good point to begin a serious evaluation. Although I have to say that some capacitors need longer than 100hrs to fully settled in. For tubes I feel 50hrs is good enough for them to settling.
As for keeping track of hours on tube. I use this to keep track hours on my KR Audio 842VHD tubes...

I just click it after each listening session. And this also help me roughly keep track other tubes in my system also, 6EA7/6EM7s on those amps, 12AX7s, 12AU7s in my pre.

I actually have 2 more of the tally to use when I change those tubes in my pre if I want.
Take care,
Buddy