Below is the code used to display the LogonHours in NetTools, the function is called for each square in the grid, the ACol and ARow defining the square that is being queried, the function will colour the square blue, if the LogonHour is set.  The function also automatically adjusts the LogonHours based on the local or user selected time zone.

void dgHoursDrawCell(TObject *Sender, int ACol, int ARow, TRect &Rect, TGridDrawState State)
{
int Index, Col,Row, Mask;
int Val, Bias;

   // use Col and Row to reflect tz offset
   Col = ACol;
   Row = ARow;

   // change start of week to Monday
   if (Row==6){
      Row = 0;
   } else {
      Row++;
   }

   if (chkLocalTime->Checked){
      Bias = tz.Bias/60;  // get local time zone, tz populated when form is loaded
   } else {
      try {
          Bias = StrToInt(cmbTZOffset->Text);  // get user selection
      }
      catch(...){
          Bias = 0;
      }
   }

   Col += Bias;  // add time zone offset

   if (Col > 23) {  // rap pointer to start of next day
      Row++;
      Col -= 24;
   }

   if (Col < 0) {  // rap pointer to end of the previous day
      Row--;
      Col += 24;
   }

   if (Row > 6) Row = 0; // rap pointer to valid data
   if (Row < 0) Row = 6;

   if (Col >=0 && Col <=7) Index=0;  // select the correct hours offset bytes
   if (Col >=8 && Col <=15) Index=1;
   if (Col >=16 && Col <=23) Index=2;

   Index += (3 * Row);  // get correct byte
   Mask = 0x1 << (Col % 8);  // create bit mask for hour based on col number

   Val = HourBuffer[Index] & Mask;  // apply mask to check if set

   if (Val){  // Val is non zero set square to blue
       dgHours->Canvas->Brush->Color = clBlue;
   } else {
       dgHours->Canvas->Brush->Color = clWhite;
   }

   dgHours->Canvas->FillRect(Rect);  // draw the square

}