It is apparent that you obtained string concatenation, and not numeric calculation. Probably you just used '+' operator on strings.
No, please see my comment to the question. Summing up objects of the type
System.DateTime
makes no sense at all; they represents points on the time axis.
Consider using
System.TimeSpan
instead. But before calculating the sum, you need to parse the string to this type. Please see all the methods named
Parse
,
ParseExact
,
TryParse
and
TryParseExact
:
http://msdn.microsoft.com/en-us/library/system.timespan_methods%28v=vs.110%29.aspx[
^].
—SA