Even if that is an oil based stain, it's not going to grab to the clearcoat of the car, I'd just be worried about the color staining it, so I'd be trying to remove it ASAP.
Good news is, if they used Thompson's deck stain, you should just be able to hose it right off, that shit is garbage even for it's intended purpose
Edit: Glen beat me to it, I'd go the paint thinner route like he suggested. It shouldn't be hot enough to affect the clear but it'll probably take off any wax you've put on the car