I think @wyone and @ray are right about run-once being preferred. I personally use manual mode for debugging purposes (testing sprinkler head, water line, wiring, etc). Otherwise, run-once can handle the timers per station.
With all of this said, like @ray said, the OpenSprinkler has the option for timers in manual mode. So, I can add this feature, if people are interested. Just let me know.