Difference between two Business days in hh:mm format

Here's my attempt at that:

using System;

class Program
{
    static void Main()
    {
       string startDate1 = "10/01/2007 10:00:00";
       string endDate1  = "10/10/2007 19:00:00";
       string dateDiff1 = BusinessTimeSpan(startDate1, endDate1);
       Console.WriteLine("The time span between {0} and {1} excluding weekends is {2} h:m", startDate1, endDate1, dateDiff1);        
       string startDate2 = "09/28/2007 10:10:00";
       string endDate2  = "10/08/2007 10:30:00";
       string dateDiff2 = BusinessTimeSpan(startDate2, endDate2);
       Console.WriteLine("The time span between {0} and {1} excluding weekends is {2} h:m", startDate2, endDate2, dateDiff2);        
       Console.ReadKey();
    }

    public static string BusinessTimeSpan(string startDate, string endDate)
    {
       string format = "MM/dd/yyyy HH:mm:ss";
       DateTime dt1 = DateTime.ParseExact(startDate, format, null);
       DateTime dt2 = DateTime.ParseExact(endDate, format, null);
       if (dt1 == dt2)
          return "00:00";
       else if (dt1 > dt2)
       {
          // reverse dates so dt1 < dt2
          DateTime dt = dt2;
          dt2 = dt1;
          dt1 = dt;
       }

       if (dt1.DayOfWeek == DayOfWeek.Saturday)
       {
          // adjust to midnight on folowing Monday 
          dt1 = dt1.AddDays(2);
          dt1 = new DateTime(dt1.Year, dt1.Month, dt1.Day);
       }
       else if (dt1.DayOfWeek == DayOfWeek.Sunday)
       {
          dt1 = dt1.AddDays(1);
          dt1 = new DateTime(dt1.Year, dt1.Month, dt1.Day);
       }

       if (dt2.DayOfWeek == DayOfWeek.Saturday)
       {
          // adjust to one second before midnight on preceding Friday
          dt2 = new DateTime(dt2.Year, dt2.Month, dt2.Day);
          dt2 = dt2.AddSeconds(-1);
       }
       else if (dt2.DayOfWeek == DayOfWeek.Sunday)
       {
          dt2 = new DateTime(dt2.Year, dt2.Month, dt2.Day);
          dt2 = dt2.AddDays(-1).AddSeconds(-1);
       }

       DateTime temp = dt1;
       int count = 0; // counts days between dt1 and dt2
       while(true)
       {
          if (temp.Year == dt2.Year && temp.Month == dt2.Month && temp.Day == dt2.Day) break;
          temp = temp.AddDays(1);
          if (temp.DayOfWeek == DayOfWeek.Saturday)
              temp = temp.AddDays(2);
          else if (temp.DayOfWeek == DayOfWeek.Sunday)
              temp = temp.AddDays(1);
          count++;
        }  
       int minutesDiff = count * 24 * 60 + (dt2.Hour * 3600 + dt2.Minute * 60 + dt2.Second - dt1.Hour * 3600 - dt1.Minute * 60 - dt1.Second) / 60;
       int hoursDiff = minutesDiff/60;
       minutesDiff = minutesDiff % 60; 
       return String.Format("{0:00}:{1:00}", hoursDiff, minutesDiff);  
    }
}