I’ve run mine 15 minutes pulling on a head space eliminator. You won’t hurt that pump. You might trip the thermal breaker but just as soon as it cools off it’ll go right back to work.
If there is a lot of gas your reading might be off a bit. I’d strain off enough to get a good test and put it in a bottle and shake the crap out of it to get the gas out. Then try to get Another reading.