How Long to Burn-In Western Electric 300Bs?

I have a new pair of reissue Western Electric 300Bs that I am running in my Morrow Audio SET amps. I read some comments in a Stereophile column published a number of years ago in which the reviewer discussed a very protracted burn-in time for the tubes. The reviewer had experienced a dramatic change in the sound of his WE 300Bs after a burn-in period of several hundred hours. He later ran into the principal at Western Electric (Charles Whitener) at a trade show and inquired about the manufacturer's recommendations with respect to burn-in of the tubes. In a follow-up column, the reviewer relayed Western Electric's suggestion that the tubes require a minimum of 500 hours of burn-in.

The Stereophile follow-up column goes on to say that the Western Electric 300Bs require a much longer burn-in period than most tubes because WE chooses not to use calcium oxide in their filament coating. WE apparently believes that calcium oxide shortens the filament life. The downside of this approach is that it apparently takes a LONG time for the filament to burn in without the calcium oxide acting to accelerate the activation of the barium in the filament coating.

For those of you running Western Electric 300Bs in single-ended amps, I would be interested in your experience with respect to burn-in. Were there truly significant changes in the sound of the WE tubes hundreds of hours into the burn-in process?

Frankly, I felt that the WE tubes sounded excellent right out of the box, and I can't imagine there will be significant improvements. Nonetheless, I'm curious about others' experience.