In Actionscript, the Unix timestamp in milliseconds is obtainable like this:
public static function getTimeStamp():uint
{
var now:Date =
For actionscript3, new Date().getTime() should work.
In PHP you can simply call time() to get the time passed since January 1 1970 00:00:00 GMT in seconds. If you want milliseconds just do (time()*1000).
If you use microtime() multiply the second part with 1000 to get milliseconds. Multiply the first part with 1000 to get the milliseconds and round that. Then add the two numbers together. Voilá.