If you 'name your price' for airfare on Priceline, your flight will depart between 6 AM and 10 PM. While the posters above seem to have had reasonable luck, frequently PL users find themselves arriving at their destinations late and departing early - effectively cutting two days off the stay at the destination.
If you can limit the number of stops, I don't think 0 is an option - it's probably more like 1-2, and 3. Another option is whether or not you're willing to fly on a prop plane.
And of course, all transactions are final. Your credit card is billed immediately if your bid is successful, and there are NO refunds or credits.