setting up a wp cron job

It depends what you mean by “I want the test.php file to be called not earlier then a specific time each day”.

Setting up a cron job is very straightforward, you just need to simply do:

<?php
register_activation_hook( __FILE__, 'prefix_activation' );
/**
 * On activation, set a time, frequency and name of an action hook to be scheduled.
 */
function prefix_activation() {
    // Schedule job for 3pm every day
    wp_schedule_event( mktime(15, 0, 0, date("n"), date("j"), date("Y")), 'daily', 'prefix_daily_event_hook' );
}

add_action( 'prefix_daily_event_hook', 'prefix_do_this_daily' );
/**
 * On the scheduled action hook, run the function.
 */
function prefix_do_this_daily() {
    // do something every day
}

What it is you decide to do inside prefix_do_this_daily is up to you.