The secret is that you must be logged in!!! Then the option of "my travel days are flexable" comes up under where you type the dates. You can then search 3 days before and after each date. It seems to work great.

Just figured out that you only have to be logged in when searching for award travel. If you want to pay for your trip just click on "more search options" under where you type in where and when and then "my dates are flexible"