Yes, that's true. It has been O(1 hour) for pretty much the entire history of Linux. And if you think about it, this makes sense. If it were significantly less than that, the development cycle would speed up so it would be easier to add capabilities, which would slow down the build. If it were significantly longer, the addition of new features would slow down until the hardware started to catch up. So the compile time acts as a sort of natural control mechanism to throttle the addition of new features.