code: def market_open(self, session, mins) -> Session:
          
          if session not in self.exch: return SessNA
          start_time = self.exch[session][0]
          return Session(start_time, shift_time(start_time, int(mins)))
docs: Time intervals for market open
  
          Args:
              session: [allday, day, am, pm, night]
              mins: mintues after open
  
          Returns:
              Session of start_time and end_time