I add my second dose right on top of my first. So my first addition would be for say 7 days, and my second for 4. I'll add my first addition, and then in 3 days add my second addition, after the 7th day I'll transfer to keg. Very interested in what others do, however. This is just the way I've done it, and don't have a better answer as to why I do it this way.