DateTime.ParseEtract (TextBox1.Text, "MM / dd / yyyy HH: mm", _cultureInfo);
Your input string doesn't have spaces between all the elements, so why does your format string?
Should be:
DateTime.ParseEtract (TextBox1.Text, "MM/dd/yyyy HH:mm", _cultureInfo);
Spaces are important, especially when using DateTime.Parse
Exact()