Watchers scan once every 10 seconds. There's no way to control this directly, although you could programatically (or via AppleScript) launch and quit the Watcher(s) as needed.
One problem I did consider when writing Watchers was that of a large file being written to the watched folder - I designed it so that the file will not be uploaded until its modification date stops changing. If the mod date remains static for long enough then it will be uploaded.
I can't think of any gotchas with your proposed scenario - hopefully it will 'just work' ...
If you have any problems/questions, I'm right here
