string st1="12:13";

     string st2="14:14";

     DateTime dt1=Convert.ToDateTime(st1);

     DateTime dt2=Convert.ToDateTime(st2);

     DateTime dt3=DateTime.Now;

     if(DateTime.Compare(dt1,dt2)>)

      msg.Text=st1+">"+st2;

     else

      msg.Text=st1+"<"+st2;

     msg.Text+="\r\n"+dt1.ToString();

     if(DateTime.Compare(dt1,dt3)>)

      msg.Text+="\r\n"+st1+">"+dt3.ToString();

     else

      msg.Text+="\r\n"+st1+"<"+dt3.ToString();

 private string DateDiff(DateTime DateTime1,DateTime DateTime2)

          {

              string dateDiff=null;

              try

              {

                  TimeSpan ts1=new    TimeSpan(DateTime1.Ticks);

                  TimeSpan ts2=new    TimeSpan(DateTime2.Ticks);

                  TimeSpan ts=ts1.Subtract(ts2).Duration();

                  dateDiff=ts.Days.ToString()+"天"

                          +ts.Hours.ToString()+"小时"

                          +ts.Minutes.ToString()+"分钟"

                          +ts.Seconds.ToString()+"秒";

              }

              catch

              {

              }

              return dateDiff;

          }

 TimeSpan ts=new TimeSpan(,,,);

     DateTime dt2=DateTime.Now.Subtract(ts);

     msg.Text=DateTime.Now.ToString()+"-"+ts.Days.ToString()+"天\r\n";

     msg.Text+=dt2.ToString();