how do you gauge and judge "timing"?

. In a broader sense, timing in acoustics relates to the duration of sounds and the time intervals between them, which are critical for clarity, intelligibility, and overall sound quality» 

"Timing" is an acoustics concepts , it can refer also to time domain analysis ...

time to google the stereophile glossary, timing The apparent instrumental ensemble (synchronism) of a performance, which is affected by system speed. See "articulation," "rhythm," "pace."

There. reading that sure helped me. I interpret it to suggest a smooth transition between drivers with a reasonably even in room tonal balance.

Snappy snare drum and fast bass drum. Doesn’t get lost during fast passages. I don’t know but that’s what I think of. 

Rolling tubes taught me a lot about PRAT - when it's there and when not and the question "why" which was never very clearly answered. It is the manipulation of seeming imperfections into something unexpectedly dancing and beautiful that is the nectar of audiophilia. In trying to enliven recorded music we get a little peek into what the musicians themselves were doing with their instruments and what the recording engineers played with albeit on a tiny scale, but that doesn't make it any less intriguing.

@audiocanada 

Good question, the best way to hear it is to have owned different sounding components to get an understanding by means of comparison.  

Timing can be found (or not found) in everything from recordings, cartridges, phono preamps, digital sources, preamplifiers, amplifiers, interconnect cables and of course speakers.

I also like to think of it as musical CONTRAST and speed / energy.  
Example- I had a Parasound 21+ amplifier that sounded anemic, lacked contrast and energy.  The notes tended to blend and just sit there.  Very dull timing and not at all accurate to live music.  

Then I bought a Pass Labs XA25- an absolute stunning difference.  The music seemed to burst out of the speakers with rapid acceleration and quickness, so much more contrast between the musical players.