You don't say how long you've been seeing this guy, or how long you've known him.
Personally, I wouldn't have him over at night after your daughter goes to sleep, just in the event that she'd wake up and see/meet him for the first time under those circumstances.
I wouldn't have him over until you've introduced your daughter to him in the light of day. I don't know how old your daughter is, but I wouldn't want my child to wake up and see a strange man in our home, or think I was hiding something from him. I'm a single mom too, although recently engaged. I definitely understand the difficulty of finding time to spend together, and at night when kids are asleep sounds like a reasonable solution, but I wouldn't be comfortable doing it until they've met.
Also, on the side of having your child meet - or not meet - a suitor, I tend to lean on the side of getting the man comfortable being with you and your child. This is your life, and it's not changing. So if he's going to be in your life, he needs to know your life, as it is. Now, before I get lambasted, I am CERTAINLY NOT suggesting that you bring every Tom, Dick, and Harry to the house to meet your child. I only recommend introducing anyone you feel is a true marriage candidate, and you don't know that in the early stages of a relationship. But I am also not a proponent of pretending to be a swinging single with no committments either. It would be dishonest to present that way, because you are not without committments, you do not have the freedom of a single person without children, and your daughter will undoubtedly remain the focus of your life. Anyone thinking about being a part of your life needs to know your life in reality. Not in pretend-to-be-single-without-committments dating world. It's a fine line to know when is the right time, but you'll know.
Best wishes.