Hi. I'm not a pro baker, but I've used lemon curd filling in my cupcakes before and didn't refrigerate them after being filled. No one has gotten sick, and they still tasted fine. Since you're just talking about overnight, I don't think it's going to hurt anything. I'm sure if I'm wrong, someone will let us know, but as I said I've done it before without problems.
11/26/11 at 4:21pm