Guide: Once the day ends, monsters such as skeletons and spiders will start shuffling toward you. Since you have a single block open from your cave entrance, skeletons could still technically hit you with their arrows, but luckily for you they are miserable shots. Spiders will also try to infiltrate your abode, but they shouldn't be able to reach you.
Once daytime hits, all monsters other than spiders will burst into flames, clearing the way for a new day of adventuring. If you see a spider, don't panic -- they won't attack you unless you attack them first.