I roasted some oats last week. I wasn't going for a super deep roast, just a toast. I spread them out on a cookie sheet and baked at 350. I checked at 10min and they weren't that roasted. At 15min, they were darkened a bit. I waited about 2min later and pulled them out, they were darked and tasted more roasty than raw oats.
I suggest keeping a handful of raw oats out next to the oven so that when you check on your roasting oats you can compare them to raw ones quickly.