This function returns the current Unix timestamp with microseconds.
The argument “get_as_float” is Optional. When set to true it specifies that the function should return a float, instead of a string.
Note: This function returns the string “microsec sec”, where sec is the number of seconds since the Unix Epoch (0:00:00 January 1, 1970 GMT),and microsec is the microseconds part. Notice that both parts are returned in units of seconds.
Note: The get_as_float parameter was added to PHP 5!