how do you gauge and judge "timing"?

There must be a new band name in here somewhere... The PRaTty Five?

@deep_333  that's not good music.

Listening to some White Zombie Thrust 75ish db. Good shnitt. Lotsa Prat up in dere! lol 

 Timing , to me, is the rythmic integrity of recorded and reproduced music.  It is a subset of the term PRaT - pace, rhythm, and timing.  The history of the term and emotional response elicited by it is well described by Paul McGowan, PS Audio in the attached link. https://m.youtube.com/watch?v=6qJrF4_8lCY.  What technically contributes to PRaT is not addressed.  Being an audiophile for over 55 years, and listening to many systems, I have established my own opinions of what contributes to a system having the quality of PRaT.  A few disclaimers first.  PRaT is a subjective emotional response to recorded and reproduced music and, as such, each of us will respond differently and have our own interpretations of what contributes to PRaT.  Second, these are my novice impressions as an audiophile, not an equipment designer.  Her are my impressions of what technically contributes to the emotional quality of PRaT:

1. Phase alignment of speaker elements to assure the leading edge of the sound waves from each element reach the listener at the same time.
2. Transient speed, leading edge, and lack of ringing contribute to clarity, and without which  will smear the sound, reducing PRaT. 
3. Dynamic response, including the reproduction of micro dynamics as well as macro dynamics seems self evident in getting feet tapping.
4. Detail, especially the ability of the system to capture harmonic decay.    This contributes greatly to natural sounding PRaT.  All instruments in an environment will have harmonic decay, contributing to us respond emotionally to PRaT.  

As Paul indicated, historically PRaT was a term developed by Linn and Naim. Note PRAT is UK slang for an incompetent or stupid person; an idiot.  I am sure some will have fun with the slang definition. 
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"It don't mean a thing if it ain't got that swing."

It's when the musicians are talking back and forth to each other and sometimes playing a little catch up to some new development that the music starts to sound ingratiatingly real. Stevie Ray Vaughn is my favorite PRATTY player because he was so adept at swinging, stretching and nipping. Hendrix comes to mind as well. Jascha Heifetz and Artur Rubenstein could swing like crazy. When Garcia and Grisman were playing together there was always suspense. When Willy went out on a limb with Trigger and then found a way back home when all appeared to be lost - that made the audience and band listen real hard. It makes for a more suspenseful and slightly dangerous performance - what a lot of us live for in trying to flesh out a life.

"Art is dangerous. It is one of the attractions: when it ceases to be dangerous, you don't want it."