As long as their is hissing it is best to wait a bit. Yet if you are not observing any other behaviors (swishing tail, ears flat, growling, lunging, yowling, howling, etc...) then it might just be a warning. Wait a few more days and see what happens, hissing by itself is not a big deal. It's when it goes beyond hissing where you want to slow down.
Oskar looks wonderful on her cat tree!! So happy she is using and enjoying it.
Oskar looks wonderful on her cat tree!! So happy she is using and enjoying it.