Nice idea. While I'm not sold on the idea of making pizza deliveries specifically, I can totally get behind the idea of delivering perishable items within a certain time-limit or you won't get paid (and you get left with a cargo hold full of biowaste). Scientific samples, corrosive goods, food, etc...
If it could be done in such a way that smaller faster ships have a significant advantage over slower large lumbering ships, then it would be great to race against the clock.