Regarding the serial port: please follow the re-programming instructions — you only need to select board and then click on Upload, there is no step to select a serial port. This is because OpenSprinkler does not have a USB-serial chip (which the standard Arduino has).
I will take a look at the timing issue as soon as I can. Meanwhile, have you considered adding a UPS backup power supply? That may be the simplest solution to the power interruption problem.