|This feature was removed completely in version 1.32.0.|
|Global object: $wgRequestTime|
|timer, initialized in WebStart.php and Maintenance.php|
$wgRequestTime is a global microtime float that is initialized early in the engine that a lot of other times are computed relative to for logging, profiling, and debugging.
A snippet from Debug.php:
global $wgRequestTime; return array( 'time' => microtime( true ) - $wgRequestTime, );