I've noticed that my little ones run less when they're chilly. First thing I'd do is check the temperature in your hedgie's house and make sure that it doesn't dip at night. Also, if there's something scary (thunderstorm, lights are on, too much noise), a hedgie may be too scared to come out. Illness can do it too. As can nails that have grown too long. Or the wheel smells funny to them (easy way to address that is to rinse and rinse with plain water... even if it smells normal to you in the first place). And there are some nights a hedgie will just decide not to run... or manages not to poop and pee all over the wheel while running which gives the illusion that no running occurred. Mostly, though, when I see a clean wheel, I worry and try to figure it out -- just like you're doing. Sooo.... check the temp, hedgie's nails, rinse the wheel, make sure the lights are out and that it's quiet... then see how it looks tomorrow morning. Or if there are any other signs things have gone awry (not eating, not pooping, belly is cool to the touch, sneezing, messy poops, etc...), then it likely suggests there's a problem.
Yes, you can tell how much they run at night if you hook up an odometer to the wheel. You can find a relatively inexpensive bike computer at places like Target/Walmart/Kmart. I believe Kalandra has done that with some/all of her wheels (??).