Q:

What does this timestamp mean

So I got a timestamp from Google API in the following format:
2012-08-21T20:19:08.452Z

My question is...What is that .452 preceding the Z?  I believe Z denotes Zulu time aka UTC, but what is that .452....Are those fractions of a second? 

A:

Yes, those are fractions of a second.  That is the ISO 8601 date format, by the way (specifically, the RFC 3339 subset of it). 
If you want to convert it to a Unix timestamp, you can use PHP's strtotime function (since you tagged this question php).