The best way to get what you're asking for is through the calculated field is tu use Derek's methode.
But if you want use a script, see thoses snippets :

procedure Form1_TableGrid1_OnChange (Sender: TObject);
begin
   TNxDateColumn(Form1.TableGrid1.Columns[0]).FormatMask :='dd.mm.yyyy';
end;

Other piedce of code :

procedure Form1_TableGrid1_OnChange (Sender: TObject);
begin
     TNxTimeColumn(Form1.TableGrid1.Columns[0]).FormatMask :='HH:mm am/pm';
end;

You will have to adapt it to your needs.

A question for my friend Derek :

If vVckus uses a report (* .fr3), will your calculated field appear there and will it be able to use it?

Regards

JB