Linux – How to rsync files / folders from a specific date forward

You need to change your find to look at files.

find /Volumes/MP_JUBBLER/testing/src/ -mmin -4 -type f 

I'm a little bit confused about what you're trying to do. Rsync, all by itself, will only transfer new/modified files. So if you transport data on a hard drive once/week, you can run rsync periodically and it will no more bandwidth than (and possibly less than) the solution you're proposing using find.

All this work with find seems like you're just duplicating features that are already there.

If you really want to use find, you don't need xargs or xargs-like features; just do this:

find ... -print | rsync ... --files-from=-

Where ... is "whatever other options you feel are appropriate". This causes rsync to read a list of files from stdin.