Creating weather background images based on day and night using the 24 hour clock. Requires new images for the night time.

hg_day_night_weather_images.php

function hg_awesome_weather_bg_ext()
{
  // 24 HOUR CLOCK:
  // LESS THAN 8 AM OR GREATER THAN 9 PM

  if( get_the_time('G') < 8 || get_the_time('21') > 9 )
  {
    return "night.jpg";
  }

  return "jpg";
}
add_filter('awesome_weather_bg_ext', 'hg_awesome_weather_bg_ext');