On my experience, it takes about 10-20 hours of loud playing (gig level). Of course, the type of sound you use affects the length of time required.
I also tried that celestion advice and played with a very loud clean sound when I tried to break in V30īs in an ENGL cab. To tell you the truth, they didn't break in for me :) I played clean chords, percussive playing and stuff like that. YMMV, once again.
In the end, I just played and after about 15 hours of playing, the speakers eased up. My advice: just play them and adjust your amp settings according to the speaker tone (less treble from amp, most likely). For me, there wasn't a sudden moment when the speakers broke in. It just happened gradually.
0.02 dollaaas.
Zaned