Having plenty of experience with several VTL amps, including the 450's, I'd say 45 minutes before they really start singing. Ditto for your other components, be they tubed or SS.
Also, don't even think about biasing your 450's til they've been on 30-45 minutes. The readings will definitely change if you don't give them enough time to warm up.
Also, don't even think about biasing your 450's til they've been on 30-45 minutes. The readings will definitely change if you don't give them enough time to warm up.