Hi Gene,
The OpenSprinkler online user manual, particularly this section:
http://rayshobby.net/?page_id=730#program
explains how to assign each station a different water time. Basically each program requires a uniform water time, but you can create multiple programs, with the same start / end / interval times, and select different stations with different water time.
Allowing stations to have different water time within a single program is being addressed in the next firmware update. For now, please use the work-around above. Thanks.