Is it illegal to park in front of a house at night and stay in the car for a couple of minutes?

Yes, because you were parked in front of a property that's not your property; on the otherhand, if law enforcements would've showed up, they would most likely question you as to why you were park in front of a house thst you don't live in, and also, tell you what were you and your girlfriend doing at the time and what made you stop?