I used Braso allot before "I knew better" and I STILL use it in the tumbler. And I don't wait a day to put the brass in. I just pour a little in, stir it around good to get it mixed well, add brass and tumble away. Make sure it gets well mixed before adding the brass or it may clump up inside the cases. (That's Bad) I have never found it to weaken brass. I’m sure if you had an analysis done by a metallurgist, they may be able to show you some degradation on a molecular level, but I don’t think it hurts enough to worry about.
I have fired these Braso cleaned cases many many more times then people say you should. At pressures way above what you should. (also,,, before I knew better). I have never split one, or even cracked a neck. And they haven’t grown excessively in length. This is just my experience and your mileage may vary so to speak