Probable cause of this is the mismatch in type of field and the data that is written to that field

in stock_move class/object you have field 'date':fields.datetime(....
and in method wich is run on validating delivery : create_chained_picking the value entered is  'date': time.strftime('%Y-%m-%d')

you can override it by writing a custom module wich will change column type from and override that method writing correct datime value like: 'date': datetime.strftime('%Y-%m-%d %H:%M:%S')
Writing only date part in datetime field will make server assume time is 00:00:00 .. and your time zone setting will make the timeshift from 00:00:00 to your time... that is why you always have 19:00:00 hrs in your delivery orders.. .

hope it helps..