I've been wanting to do nothing but top cropped beers. I don't do full open fermentations, but just leave the lid sit on top of the bucket. I snap it down after about 3 days after harvesting.I always give my beers a gentle but firm stir after top cropping to keep the yeast roused. I believe this is what he meant by "beating back" the yeast.
I usually skim the brown crud when I see it forming, usually about 24 hours, then again at maybe 36 hours, and then maybe one more time before I start seeing a creamy texture to the krausen. That's when I top crop yeast to use. Anywhere between 48 and 72 hours typically. I don't get diacetyl, so it hasn't been an issue. I'm thinking that as long as the yeast looks thick and creamy, it's ready to top crop. And give it another gentle but firm stir.
My last batch of bitter was split between 1318 and 1968. Both carboys were well swirled 3 days after pitching. I didn't notice any diacetyl in the final beers, and I know I've gotten it from 1968 when I haven't swirled. Fermentation temps never exceeded 70o.
I'm starting to think that diacetyl is an indicator of a need to change your process, and perhaps that doesn't mean a diacetyl rest. I've heard that German breweries don't do rests, that they are able to control fermentation temps/yeast health to the point that the yeast will happily remove diacetyl while still at cold temps. I recently purchased CAMRA's "Brew Real Ale at Home" book, and the author mentioned rousing/beating the yeast back into suspension being a mechanism for reducing diacetyl. As homebrewers, we may always need to do diacetyl rests with lagers, but ales? I think we can nail those if we try. British brewing techniques seem to transfer to homebrew scales much more readily.
I'm considering going all open fermentation on my British beers.
Right now I'm doing some "lager" styles with wy1007. It's just too fun to top crop and so easy to keep yeast strains going for a long time with clean healthy yeast. I even use yeast from dark beers for lighter styles because the krausen, after all the crud is skimmed, is nice and clean. It's darker, but I don't think it's a problem.