I note that the question is "How do you define time". I prefer to chase the question a little further. Ie. what is time? In other words, a definition that we all can live with. (define live)
Hawkings et al have come up with a definition of time that makes certain assumptions. If a Bibical chaos ever existed I suspect that there would still have been some chronological events.
In a "Brief history of time" Hawkings !assumes! a beginning (end of chos). He cannot show this nor can anyone else unfortunetly
He also !assumes!, with good reason I am sure, that time cannot exist without change.
That is where we part company. Merely because change gives us humans a way to document time then time, by that definition, is merely a way to document change. A rather circular arguement. For another one read St.Thomas Aquinas who used the evidence that we exist to show that a God must also exist. Simply because we have the facility of imagination. This also a Buddist tenet. (This is but an illusion, reality consists of what we imagine)
But yet it is probable that time exists. The principle of causuality, the evidence of gamma particles whilst traversing space-time, and my being late for supper all are strong indications that time really does exist, probably on a universal scale if not a cosmic one.
The definition called spacetime which uses the speed of light (c) to calculate both speed and distance is similarly lacking. Or circular as a matter of opinion
OK-- Thius learned company has held out on me long enough. What is IT