Draw rectangle around range of bars by hours

strontiumDog:

The trouble is at the right-hand, nascent end of the chart. If my window is 1600-0800, if the time is e.g. 2300, the indicator won't have drawn the rectangle for the most recent time yet, as a bar with TimeHour()=8 won't have arrived yet.

Realising this, it meant that I need to create a rectangle at endOfTradingDay, and then ObjectModify point 1 of the rectangle every bar,

You've answered your own question. If the current bar is in the window, find the window start, the low and high, create or modify the rectangle.

#define HR2400 (PERIOD_D1 * 60)  // 86400 = 24 * 3600
#define INDEX   uint
#define SECONDS uint
SECONDS     time(datetime when=0){        if(when == 0) when = TimeCurrent();
   return SECONDS(when % HR2400);
}
datetime    date(datetime when=0){        if(when == 0) when = TimeCurrent();
   return datetime(when - time(when) );
}
/*
datetime    tomorrow( datetime when=0){   if(when == 0) when = TimeCurrent();
   return date(when) + HR2400;
}
*/
INDEX       iYesterday(datetime when=0){  if(when == 0) when = TimeCurrent();
   return iBarShift(_Symbol, PERIOD_CURRENT, date(when) - 1);
}
datetime    yesterday(datetime when=0){
   return Time[iYesterday(when)];
}
bool        in_range(SECONDS beg, SECONDS end,
                        datetime when=0){ if(when == 0) when = TimeCurrent();
   SECONDS  tod   = time(when);
   return beg < end ? beg <= tod && tod < end : !in_range(end, beg, when);
}
//////////////////////////////////////////////////////////////////////////////
   #define HRBEG 57600 // 1600
   #define HREND 28000 // 0800
   for(INDEX iBar=...){
      if(in_range(HRBEG, HREND, Time[iBar]) ){
         datetime bod   = date(Time[i]);     SECONDS  tod = time(Time[iBar]);
         if (tod < HRBEG)  bod = yesterday(bod);
         INDEX    iBeg  = iBarShift(_Symbol, PERIOD_CURRENT, bod + HRBEG);
         int      n     = iBeg - iBar + 1;
         INDEX    iLo   =  iLowest(_Symbol, PERIOD_CURRENT, MODE_LOW,  n, iBar);
         INDEX    iHi   = iHighest(_Symbol, PERIOD_CURRENT, MODE_High, n, iBar);
         draw_rectangle(PREFIX+Time[iBeg], Time[iBeg],  Low[iLo], 
                                           Time[iBar], High[iHi]);
      }  // in_range
   }  // for

Wrong except on the D1	INDEX iYesterday(datetime when=0){ if(when == 0) when = TimeCurrent(); return iBarShift(_Symbol, PERIOD_CURRENT, date(when) - 1); }
Correction	INDEX iYesterday(datetime when=0){ if(when == 0) when = TimeCurrent(); datetime today = date(when); return iBarShift(_Symbol, PERIOD_CURRENT, date(today - 1)); }

Wrong except on the D1

INDEX       iYesterday(datetime when=0){  if(when == 0) when = TimeCurrent();
   return iBarShift(_Symbol, PERIOD_CURRENT, date(when) - 1);
}

Correction

INDEX       iYesterday(datetime when=0){  if(when == 0) when = TimeCurrent();
   datetime today = date(when);
   return iBarShift(_Symbol, PERIOD_CURRENT, date(today - 1));
}