Hey, congrats on the tough workout. I just did 60 minutes @ 245 W myself, and that was with some breaks. Doing it for 150 minutes continuously would be unbearable!
I wondered if I should tell you that you might want to set the target a little lower, because you get no credit at all when you’re below. But it looks like you figured that out yourself.
Yes, 268 W average, but only 82% above 255 W makes sense. It indicates that you weren’t perfectly stable, which is exactly the nature of riding outdoors.
It really is tougher than it sounds to stay above target power for a target duration!
By the way, it sounds like you were determined to ride continuously for 150 minutes, and that when you were below target you were still close. So of course you can take that average power as evidence that you reached your workout goal. In this sense you didn’t really need the app. But the app becomes more useful in the cases where you can’t do your target duration continuously. Then it will keep track of your completed duration, so you don’t have to.