im recently working with the DateTimeNow sketch (I found one in the web, hope it's a good one)
when I load it once it is working
but when I try to load it into another DS1307 it loads it with no errors
but time is wrong, like 5 minutes back
then I load it again (after disconnecting and connecting UNO to my PC and restarting IDE)
and It shows like 2 hours ahead
but when I burn the bootloader and load the sketch it's all good.