I definately depends on the volume you play at, but still I wouldn't agree it takes anything like 150 hours.
When I bought some G12H-30s for my Bluesbreaker back in 2001 they were solid in the bass, really snarly in the mids and the treble was pretty angry too, I certainly wouldn't say they were bright. I noticed after a few practices (maybe 20 hours most) that the mids/treble had settled down and become smoother, plus the speaker sounded altogether less stiff.
With the 55Hz bass cone G12M-25s I had in my 4x12, they were the same story - a little harsh at first, but didn't take long for that silky smooth compressed mids/top end to come out.
:twisted: