Finding Textbox fields in Templates

I have 2 textboxes that I am using for StartDate and EndDate in DateTime format, I am using DetailsView with Insert and Edit Templates, I was provided this code by "compguy2100", in order to make sure that the EndDate comes after the StartDate by at least 1 Minute.  What I can't figure out is how to get the code to find the textboxes in question so it can validate them.  I've used Detailsview.findcontrol with other controls however they are used with Item updating or inserting.  I need this to run once the user has either entered a Date and Time and tabbed to a different dataentry cell.  I've tried to use this code in the TextChanged event with no luck.
 
Dim StartDate As Date
        Dim EndDate As Date
        Dim Difference As TimeSpan

     &nb ...