Schedules a hook which will be executed once by the WordPress actions core at a time which you specify. The action will fire off when someone visits your WordPress site, if the schedule time has passed

Schedule an event one hour from now:

function do_this_in_an_hour() {

    // do something
add_action( 'my_new_event','do_this_in_an_hour' );

// put this line inside a function, 
// presumably in response to something the user does
// otherwise it will schedule a new event on every page visit

wp_schedule_single_event( time() + 3600, 'my_new_event' );

// time() + 3600 = one hour from now.