Restoring from Yosemite Time Machine backup on Mavericks
It's unlikely that this will work - and any software that was updated will probably not understand its settings file (e.g. Mail, Messages and the like). Also, restoring everything would replace system files with Yosemite versions.

You could go into Time Machine and pull out documents and content you have created/updated while running Yosemite, and that should work OK. But restoring settings and the system is highly unlikely to end happily.

Definitely not recommended.