Bleach mainly sanitizes and speeds removal of tannins. It doesn't speed up the time to waterlog wood, so far as I've ever noticed. I don't really measure the bleach. I fill a five gallon bucket & pour in some bleach, give it a quick stir and submerge the wood using whatever I've got handy if it won't sink below the surface. I pour bleach by eye because I can never find the measuring cup when I want it
, and I do the same for the laundry too. It's about a half cup of bleach to the 5 gallon pail.
It will prevent soaking water from getting smelly too. Standing water left for awhile becomes stagnant and can start to smell, especially if it has any organics in it. Wood is an organic, and bleach kills the odour causing bacteria in stagnant water the same way it kills dangerous bacteria in drinking water.
Tannins are what turn water brown or yellow. They'll continue to leach for some time, but bleach will take a lot of them out fairly quickly. It can also lighten the surface colour of dark wood. Well weathered wood isn't going to show much, if any, colour change at all.
I sometimes lighten very dark wood pieces, either so that Nerite snail eggs won't show as much, or to make more contrast between one piece of wood and another. If I don't like the way it turns out, coarse steel wool or sandpaper will rub off the bleached outer layer and reveal the original colour underneath again.