OK 25-30 hours. As expected with any good KT88, they have really opened up. The other KT88 I have run as drivers in this amp is the now unobtanium Shuguang WEKT88, which was their best KT88 right before the factory shut down. The Shuguang WE series WE6SN7 and WEKT88 were very rich and full sounding. They leaned towards the warm side of things, but still had good detail. The Linlai E-6SN7 and this KT88-D are decidedly neutral sounding with great detail and very tight bass. I would not call them warm, but rather very neutral. Don't get me wrong, they are still tubes, and not solid state sounding at all. But they are not overly romantic. The JJ KT88 is a good tube, but in my KT88 amp it sounded just a little unnatural with emphasis of certain parts of the frequency spectrum. Very subtle, but designed to sound very alive and grab your attention. The Linlai offererings are just very neutral. They do everything well with great detail and slam, but they are not overly warm like the Shuguang WE series, nor do they draw attention to themselves a bit like the JJ. I really like the Linlai WE300b exact Western Electric copy. It is also a wonderful tube to my ear.
So those are my opinions. You can take or leave them. A data point for you all:)
Happy listening