microtime returns the current Unix timestamp with microseconds. This function is only available on operating systems that support the gettimeofday() system call.
For performance measurements, using hrtime is recommended.
If used and set to true, microtime will return a float instead of a string, as described in the return values section below.
By default, microtime returns a string in the form "msec sec", where sec is the number of seconds since the Unix epoch (0:00:00 January 1,1970 GMT), and msec measures microseconds that have elapsed since sec and is also expressed in seconds.
If as_float is set to true, then microtime returns a float, which represents the current time in seconds since the Unix epoch accurate to the nearest microsecond.