Found some info here:
https://discussions.apple.com/thread/3963202
Blocking TCP 5223 and the following IP ranges:
17.173.0.0/16
17.178.0.0/16
17.133.0.0/16
Again with the caveat that this will likely take down multiple Apple services as the port is used for the Apple Push Notification Service and the ranges are big.
Also found a blog of someone who studied the Facetime protocol in detail in 2010:
http://www.packetstan.com/search?q=facetime
Might have changed since then...
I also found some info on the Aruba website that they at least can identify the conversations to optimise QoS (not with the intention to block anything).