docs: def _get_earliest_valid_timestamp(self, symbol, interval):
          """Get earliest valid open timestamp from Binance
  
          :param symbol: Name of symbol pair e.g BNBBTC
          :type symbol: str
          :param interval: Binance Kline interval
          :type interval: str
  
          :return: first valid timestamp
  
          """
          kline = self.get_klines(
              symbol=symbol,
              interval=interval,
              limit=1,
              startTime=0,
              endTime=None
          )
          return kline[0][0]