wp_schedule_event

register_activation_hook( __FILE__, 'my_activation' );
add_action( 'my_hourly_event', 'do_this_hourly' );
 
function my_activation() {
    wp_schedule_event( time(), 'hourly', 'my_hourly_event' );
}
 
function do_this_hourly() {
    // do something every hour
}

register_deactivation_hook( __FILE__, 'my_deactivation' );
 
function my_deactivation() {
    wp_clear_scheduled_hook( 'my_hourly_event' );
}