@rhldr: sounds like a problem with the RTC. To check whether it’s a problem with the NTC sync result or RTC, you can go to the Options page, turn off ‘NTP sync’, and set a time manually. Then see if the time drifts significantly (it will probably drift a few minutes over a few days, that is normal). If the time is significantly off, then it’s an RTC problem; if not, it’s a problem with incorrect NTP sync result.
@old_: check the time zone settings. Because OpenSprinkler doesn’t automatically detect day light saving time, you will need to manually change the time zone settings to account for DST.