Initialize all dates properties

def _init_dates(self):
        """Initialize all dates properties
        """
        if self.total_transactions == 0:
            return None
        self.epoch_start = Result.select(Result.epoch).order_by(Result.epoch.asc()).limit(1).get().epoch
        self.epoch_finish = Result.select(Result.epoch).order_by(Result.epoch.desc()).limit(1).get().epoch
        self.start_datetime = time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(self.epoch_start))
        self.finish_datetime = time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(self.epoch_finish))