Thanks @jpearman. For now I’ll use the Rotation.changed() and then use the Timer.system() to act as a timestamp, although this is probably slightly delayed from what the actual timestamp would be. Doing it this way I’m seeing an average of 10ms 
Related to the changed() callbacks, I had noticed previously that for the older 3-wire ports there was a filter on when changed gets called ( What is criteria to calling analog_in.changed()? - VEX V5 Technical Support - VEX Forum. Wondering if that applies to other sensors like Rotation sensor? I’ll see at least try to see if I can get it to register a 1 LSB rotation.
Nick