In our experience with the dogs, Baytril is pretty fast-acting, but it might take a couple of days. We've never had it prescribed for a respiratory infection though--mostly it's been for UTIs.
Hope Baci is better soon, poor dear!
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."