wp_shortcode_my_time_configurable.php

<?php
// My time shortcode [mytime timezone="Europe/Amsterdam" format="h:i A"]
// You can also edit the defaults on lines 7 & 8, then you can just use [mytime] to show your current time
add_shortcode( 'mytime', 'imw_my_time' );
function imw_my_time( $atts ) {
	$atts = shortcode_atts( array(
		'timezone' => 'Europe/Amsterdam',
		'format' => 'h:i A'
	), $atts, 'mytime' );

	$timezone = new DateTimeZone( $atts['timezone'] );
	$return = wp_date($atts['format'], null, $timezone );
	return $return;
}