Quick Hack to allow any folder to be a TimeMachine Destination

Apple doesn’t let you use a shared folder as a time machine destination in regular OSX (you can buy server and get that functionality), only a full volume or Time Capsule.

But you  can use this command line trick:
0) This assumes your Folder exported is called TimeMachine
1) – AFP mount your TimeMachine share via Command-K on the Mac you want to back up.
2) Try this. It will probably fail with an error about locking:
sudo tmutil setdestination /Volumes/TimeMachine

3) On the server you want to back up to, run
defaults write \
/private/var/db/dslocal/nodes/Default/sharepoints/TimeMachine.plist \
"timeMachineBackup" '(1)'

4) Rerun
sudo tmutil setdestination /Volumes/TimeMachine

Validate you can start your backup with:
tmutil startbackup