wp-includes/class-wpdb.php:3920Starts the timer, for debugging purposes.
true public function timer_start() { $this->time_start = microtime( true ); return true; }Introduced in 1.5.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wpdb.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.