Could be just some simple mistake with column references.
Names Default To Here(1);
dt = New Table("Untitled 5",
Add Rows(3),
New Column("DateTime", Character, "Nominal", Set Values({"21/10/24/15:21", "21/10/24/14:21", "20/09/20/15:20"}))
);
/*
other solutions
a = "21/10/24/15:21";
//other solution with Regex
Show(Regex(a, "^(.{8})(.)(.*)$", "\1 \3"));
//using Words and Concat Items
Show(Concat Items(Words(a, "/")[1 :: 3], "/") || " " || Word(4, a, "/"));
//Using Contains to get last "/" and then Substr()
lastIdx = Contains(a, "/", -1);
Substr(a, 1, lastIdx - 1) || " " || Substr(a, lastIdx + 1);
*/
dt << New Column("Compatible DateTime", Formula(Left(:DateTime, || " " || Right(:DateTime, 5)));
(Note that the new column won't be Numeric Continuous without some extra jsl)
-Jarmo