Dunno about other people, but sometimes I pre-write my comments. Either when the chapter comes out early in another language, like Spanish, or when I MTL the raws.
You can simply follow the example of "Thanks for the chapter" experts, they're ready to comment anytime. About the PS, anything that's not official grants you staff's ire, so the trick is not "watching" it, but a different verb.
Check out everythingmoe for more info I guess.