I don't know this particular camera, but most recent lenses do not have a precise infinity stop any more because of thermal changes among other things, so they tend to focus past infinity. So what you will need to do is find something to focus on, and then turn off the AF.
I think generally, since DOF increases with distance, if you can find a target within a few hundred feet on which to focus, you'll be fine. It's better to err a bit on the close side than to overshoot.
If you have time, and if you can see what you're doing at night, you might try focusing at great distance during the day and marking the lens, or just getting a feel for how much to back off from the infinity stop.
