Yardeen Electronic Water Timer Irrigation System Waterproof Rain Delay Function Color Blue

Can anyone explain how to program this? I turned the dials to every 12 hours and 5 minutes, but its not coming on unless I do manual.

I just brought one of this. But im having trouble opening the battery compartment. It felt stuck. I wondered if anyone else have this problem?

Changed batteries now the valve just keeps rotating and the dials seem to have no effect, is there a reset aside from that on the left dial?

Will this work with a gravity feed watering system connected to a 275 gallon reservoir? (will not have 40+ pounds of water pressure)