What he means is, Gates time is so much more valuable to him than his money is to him, where most people time or money might be more valuable than the other, but not to such an extreme. My time is more valuable to me, but there is only so much money I'm willing to spend on convenience. Gates however would probably be willing to spend thousands of dollars on convenience that would seem like huge waste to the rest of us.

He makes the point that despite his time being so much more valuable to him that he is still willing to spend his time doing good things instead of just having a stress free easy life.