wp_schedule_event only when admin is visited

In your event callback function check to see if the user id the admin then run the function else just reschedule it. So using the example from the codex’s page you linked in the question it would be something like this:

function my_activation() {
    if ( !wp_next_scheduled( 'my_hourly_event' ) ) {
        wp_schedule_event(time(), 'hourly', 'my_hourly_event');
    }
}
add_action('wp', 'my_activation');

function do_this_hourly() {
    // do something every hour only if this is the admin
    if (!current_user_can('administrator')){
        // time()+1800 = 1/2 hour from now.
        wp_schedule_single_event(time()+1800, 'my_hourly_event');
        return;
    }else{
        //do your thing
    }
}