ambiguous git-log date and timestamp syntax

The docs are a little vague on exactly what your options are when specifying dates. If someone can provide me some details on this i'll make a patch for the docs.

--since=date, --after=date
	Show commits more recent than a specific date.
--until=date, --before=date
	Show commits older than a specific date.
--max-age=timestamp, --min-age=timestamp
	Limit the commits output to specified time range.

 From what i can tell it seems that dates can be specified relatively,  
e.g. "2 hours ago", or with any ISO 8601 or RFC 2822 date syntax. Is  
this correct, and are there any docs on specifying relative dates?

I can't find any details on what the "timestamp" format should be. Can someone point me in the right direction?

-Kate == masukomi