wp-server-timing-quick-hack-template.php (using Performance Lab Server-Timing API)

wp-server-timing-quick-hack-template.php

<?php

function my_func() {
	global $some_metric_global;

	if ( ! isset( $some_metric_global ) ) {
		$some_metric_global = 0.0;
		add_action(
			'wp_footer',
			function() {
				perflab_server_timing_register_metric(
					'some_metric_global',
					array(
						'measure_callback' => function ( $metric ) {
							global $some_metric_global;
							$metric->set_value( $some_metric_global * 1000.0 );
						},
						'access_cap'       => 'exist',
					)
				);
			}
		);
	}

	$start = microtime( true );

	// More logic...

	$some_metric_global += microtime( true ) - $start;
}