DateUtils Calculations

I need to calculate the time (period) a student spends reading an eBook.
In the Main Module I have a Process_Global variable:

Code:

  Dim MyBookStart As Long  

When the eBook loads, I save to MyBookStart variable:

Code:

  DateTime.DateFormat = "dd-MM-yyyy HH:MM:ss"
        Main.MyBookStart = DateTime.Date(DateTime.Now)  

and receive this Error:

Code:

  java.lang.NumberFormatException: Invalid double: "03-09-2016 19:09:57"  

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