The MarketOpenHours.mqh file checks the Market Open Hours against the server time at the broker. Its input is only the Symbol name as string type. As a result you get a bool, true - the market is open, false - the market is closed. In the following image i show the Open Hours of my broker DarwinEx for the symbol EURUSD.

You can see how different these open times are on different weekdays. So here is your include file:

//+------------------------------------------------------------------+  //|                                              MarketOpenHours.mqh |  //|                                        Wolfgang Melz, wm1@gmx.de |  //|                                                 https://melz.one |  //+------------------------------------------------------------------+  #property copyright "Wolfgang Melz, wm1@gmx.de"  #property link      "https://melz.one"    //+------------------------------------------------------------------+  //| MarketOpenHours                                                  |  //+------------------------------------------------------------------+  bool MarketOpenHours(string sym) {    bool isOpen = false;                                  // by default market is closed    MqlDateTime mdtServerTime;                            // declare server time structure variable    datetime dtServerDateTime = TimeTradeServer();        // store server time     if(!TimeToStruct(dtServerDateTime,                    // is servertime correctly converted to struct?                     mdtServerTime)) {      return(false);                                      // no, return market is closed    }      ENUM_DAY_OF_WEEK today = (ENUM_DAY_OF_WEEK)           // get actual day and cast to enum                              mdtServerTime.day_of_week;      if(today > 0 || today < 6) {                          // is today in monday to friday?      datetime dtF;                                       // store trading session begin and end time      datetime dtT;                                       // date component is 1970.01.01 (0)      datetime dtServerTime = dtServerDateTime % 86400;   // set date to 1970.01.01 (0)      if(!SymbolInfoSessionTrade(sym, today,              // do we have values for dtFrom and dtTo?                                 0, dtF, dtT)) {        return(false);                                    // no, return market is closed      }      switch(today) {                                     // check for different trading sessions        case 1:          if(dtServerTime >= dtF && dtServerTime <= dtT)  // is server time in 00:05 (300) - 00:00 (86400)            isOpen = true;                                // yes, set market is open          break;        case 5:          if(dtServerTime >= dtF && dtServerTime <= dtT)  // is server time in 00:04 (240) - 23:55 (86100)            isOpen = true;                                // yes, set market is open          break;        default:          if(dtServerTime >= dtF && dtServerTime <= dtT)  // is server time in 00:04 (240) - 00:00 (86400)            isOpen = true;                                // yes, set market is open          break;      }    }    return(isOpen);  }    //+------------------------------------------------------------------+  

The first part checks for the weekday, Mon - Fri to allow opening trades and trailing stop during the week. In the switch command the actual server time is checked against the broker's symbol session.

Implications:

• If you run this script on every tick or every minute, it will give the exact open hours according to the broker's server like you see in the above image.
• If you run this script every 5 minutes on my broker account, it is correct only on Monday 00:05 - 00:00
• If you run this script on the open of each new bar, the first bar of every weekday get false, market closed also for the last bar on Friday
• If you run this script on PERIOD_D1, PERIOD_W1, PERIOD_MN1 it will not give a true signal for my broker because it runs at 00:00 and market open is at 00:04