How come spiders come out day and night?

Some Spiders specialize in daytime hunting. Jumping spiders, for instance, have very good vision and they use it to detect prey from a distance. They could not hunt well at all during the night time.

Some spicers specialize in night time hunting. There are spiders that build a web at dusk and then take it all down when the sun comes out in the morning. They hunt at night because they are much safer from things like birds.

Some spiders may hunt whenever something tasty comes along. Wolf spiders may prefer to hunt at night, but if one were taking shelter under a rock and a tasty cricket would come along the spider would probably gobble it up. Some web weaving spiders have a sort of telegraph line between their spiral web and a hideout where they wait for something to blunder into the web. They probably hang out in their shelter, but come out whenever they get prey in their webs.