Calculate Business Hours

public static double CalculateBusinessHours(DateTime dtStart, DateTime dtEnd)
   {
       int StartingHour = 9;
       int EndingHour = 18;

       // initialze our return value
       double OverAllMinutes = 0.0;

       // start time must be less than end time
       if (dtStart > dtEnd)
       {
           return OverAllMinutes;
       }
       DateTime ctTempEnd = new DateTime(dtEnd.Year, dtEnd.Month, dtEnd.Day, 0, 0, 0);
       DateTime ctTempStart = new DateTime(dtStart.Year, dtStart.Month, dtStart.Day, 0, 0, 0);

       // check if startdate and enddate are the same day
       bool bSameDay = (ctTempStart == ctTempEnd);

       // calculate the business days between the dates
       int iBusinessDays = GetBusinessDays(ctTempStart, ctTempEnd);

       // now add the time values to our temp times
       TimeSpan CTimeSpan = new TimeSpan(0, dtStart.Hour, dtStart.Minute, 0);
       ctTempStart += CTimeSpan;
       CTimeSpan = new TimeSpan(0, dtEnd.Hour, dtEnd.Minute, 0);
       ctTempEnd += CTimeSpan;

       // set our workingday time range and correct the first day
       DateTime ctMaxTime = new DateTime(ctTempStart.Year, ctTempStart.Month, ctTempStart.Day, EndingHour, 0, 0);
       DateTime ctMinTime = new DateTime(ctTempStart.Year, ctTempStart.Month, ctTempStart.Day, StartingHour, 0, 0);
       Int32 FirstDaySec = CorrectFirstDayTime(ctTempStart, ctMaxTime, ctMinTime);

       // set our workingday time range and correct the last day
       DateTime ctMaxTime1 = new DateTime(ctTempEnd.Year, ctTempEnd.Month, ctTempEnd.Day, EndingHour, 0, 0);
       DateTime ctMinTime1 = new DateTime(ctTempEnd.Year, ctTempEnd.Month, ctTempEnd.Day, StartingHour, 0, 0);
       Int32 LastDaySec = CorrectLastDayTime(ctTempEnd, ctMaxTime1, ctMinTime1);
       Int32 OverAllSec = 0;

       // now sum-up all values
       if (bSameDay)
       {
           if (iBusinessDays != 0)
           {
               TimeSpan cts = ctMaxTime - ctMinTime;
               Int32 dwBusinessDaySeconds = (cts.Days * 24 * 60 * 60) + (cts.Hours * 60 * 60) + (cts.Minutes * 60) + cts.Seconds;
               OverAllSec = FirstDaySec + LastDaySec - dwBusinessDaySeconds;
           }
       }
       else
       {
           if (iBusinessDays > 1)
               OverAllSec =
               ((iBusinessDays - 2) * 9 * 60 * 60) + FirstDaySec + LastDaySec;
       }
       OverAllMinutes = OverAllSec / 60;

       return OverAllMinutes / 60;


   }

public static DateTime AddBusinessDays(DateTime dt, int nDays)
   {
       int weeks = nDays / 5;
       nDays %= 5;
       while (dt.DayOfWeek == DayOfWeek.Saturday || dt.DayOfWeek == DayOfWeek.Sunday)
           dt = dt.AddDays(1);

       while (nDays-- > 0)
       {
           dt = dt.AddDays(1);
           if (dt.DayOfWeek == DayOfWeek.Saturday)
           {
               dt = dt.AddDays(2);
           }
       }
       return dt.AddDays(weeks * 7);
   }

   private static int GetBusinessDays(DateTime ctStart, DateTime ctEnd)
   {
       TimeSpan ctp = ctEnd - ctStart;
       int iDays = ctp.Days + 1;
       int iWeeks = iDays / 7;
       int iBusDays = iWeeks * 5;
       int iRem = iDays % 7;
       while (iRem > 0)
       {
           // no sunday, no saturday
           int iStartDay = (Int32)Enum.Parse(typeof(DayOfWeek), ctStart.DayOfWeek.ToString());
           if (iStartDay != 1 && iStartDay != 7)
           {
               iBusDays++;
           }
           TimeSpan time1 = new TimeSpan(1, 0, 0, 0);
           ctStart += time1;

           iRem--;
       }
       return iBusDays;
   }

   private static Int32 CorrectFirstDayTime(DateTime ctStart, DateTime ctMaxTime, DateTime ctMinTime)
   {
       Int32 daysec = 0;

       if (ctMaxTime < ctStart) // start time is after max time
       {
           return 0; // zero seconds for the first day
       }
       int iStartDay = (Int32)Enum.Parse(typeof(DayOfWeek), ctStart.DayOfWeek.ToString());
       if (iStartDay == 1 && iStartDay == 7)
       {
           return 0;
       }
       if (ctStart < ctMinTime) // start time is befor min time
       {
           ctStart = ctMinTime; // set start time to min time
       }
       TimeSpan ctSpan = ctMaxTime - ctStart;
       daysec = (ctSpan.Days * 24 * 60 * 60) + (ctSpan.Hours * 60 * 60) + (ctSpan.Minutes * 60) + ctSpan.Seconds;
       return daysec;
   }
   private static Int32 CorrectLastDayTime(DateTime ctEnd, DateTime ctMaxTime, DateTime ctMinTime)
   {
       Int32 daysec = 0;

       if (ctMinTime > ctEnd) // start time is after max time
       {
           return 0; // zero seconds for the first day
       }
       int iEndDay = (Int32)Enum.Parse(typeof(DayOfWeek), ctEnd.DayOfWeek.ToString());
       if (iEndDay == 1 && iEndDay == 7)
       {
           return 0;
       }
       if (ctEnd > ctMaxTime) // start time is befor min time
       {
           ctEnd = ctMaxTime; // set start time to min time
       }
       TimeSpan ctSpan = ctEnd - ctMinTime;
       daysec = (ctSpan.Days * 24 * 60 * 60) + (ctSpan.Hours * 60 * 60) + (ctSpan.Minutes * 60) + ctSpan.Seconds;
       return daysec;
   }