I will add one comment to Rodman's advice, which is generally accurate.
I own the Manley 50's, which are a variant of the Tiny Triodes. In my experience, for adjustment accuracy, you defintely do want the tubes to reach thermal stability.
However, with that said, if you have a tube that runs really hot or (worse) is approaching failure and runs on, then if this is not caught quickly, you definitely WILL take out a fuse (which is an odd duck as fuses go, at least in the Manleys). I have learned (from experience) that when biasing with unknown tubes, that I am ready with multimeter in hand when I turn the amp on, and I watch the bias current while the amps warm (repeatedly), and then in increments until reaching thermal stability.
I check immediately upon turn on (a really bad tube will exceed specs almost instantly), then after a couple of minutes, then at 5 minutes, then at 30 minutes, and then,
lastly, after an hour.
It is a very easy procedure, and doing it repeatedly as noted above is really simple.