If you have Data format on the fields you want to compare.
You can know for sure the field will be in a datetime format.
for more info on data format of fields/rows/columns:
format-a-date in excel[
^]
then you could do DateTime.Parse(your field).
When you have two instances of DateTime structure you can use operators "==", "!=" and ">", "<", ">=", "<=" in the sense "later", "earlier", "not earlier", "not later", respectively. Also, you can use subtraction operator ("-") which returns the result in the form of System.TimeSpan. This is a comprehensive set of operators to cover all your comparison needs.