Use cron to schedule events in your blog

if (!wp_next_scheduled('do_hook')) {
wp_schedule_event( time(), 'hourly', 'my_task_hook' );
}
add_action( 'do_hook', 'do_function' );
function do_function() {
wp_mail('you@wpsnipp.com', 'Automatic email', 'Hello, this is an automatically scheduled email from WordPress.');
}