The blue "guys" are actually bottles haha
Well, it doesn't really have to be this dark to give the idea it's at night. Like Dusty said blue and purple are great colors for darkness;
here's an really simple edit to show you what I mean, still looks like night, right?
Right now the pixels look very messy, especially on the wall. I don't know if the yellow is supposed to be light coming from the moon or light cast by a streetlatern, but it doesn't look right in my opinion.