I put it in right away. Ours aren't cups, just that metal "nipple" as I showed. They'll start pecking at it on their 2nd or 3rd day. I wait a few more days to be sure the majority appears to be drinking from it.Do you use nipple waterers right away? I've found that I have to wait a few weeks to use my cup nipple waterer since they aren't strong enough at first to peck it hard enough to get water out. I also wonder if it is nipple type dependent.
I'd guess one bottle for every 12-15 chicks is good. We've had 30 or so many times and put two bottles in.
And yes, three weeks or so before they can do the horizontal ones.