Mac wakes up from sleep every two hours on Mac OS X Yosemite
Since com.apple.mDNSResponder.plist got replaced by com.apple.discoveryd.plist after Yosemite Beta, there is another solution for your Problem.

All you have to do is to run following command in your terminal:

sudo /usr/libexec/PlistBuddy -c "Add :ProgramArguments: string --no-multicast" \ 
         /System/Library/LaunchDaemons/com.apple.discoveryd.plist    


And reboot your system and it should be gone.

Like also described here: http://ispire.me/fix-yosemite-rtc-alarm-wakeup-issue/

You just have to know that services relying on multicast might not work properly anymore after this change.