formatting time from a variable

DateTime dt6 = DateTime.ParseExact(strvalue.Trim(), "hh:mm", null);                                                      DateTime Test4 = DateTime.ParseExact(strvalue.Trim(), "hh:mm", null);                                                          if(Test4!=Convert.ToDateTime(Test4.ToString("hh:mm"))) message= "Error" i get the time vvale in strvalue.Trim() , if the value is something liek 100 or anything which is not a valid time it shld go in the if condition