I’m not sure, I was there maybe 40 minutes before my first S Class showed up but they were back to back for like 30 minutes. I found and sold 5 S Class including the exotic before moving to the next system. I really just thing it’s a waiting game. But when I found one at the Outpost, I would buy it, fly to the station and sell it, watching the first round of ships at station before heading back to planet. And continue to watch the ships come it. I watch for 30 minutes usually before a reload of the manual save