Other simple option is to use Left()
Names Default To Here(1);
str = "12/9/2023 19:05:57:754";
res = Left(str, Length(str) - 4);
and if you really want to get the date and time without milliseconds (not string without last 4 characters) you can also use Word
Names Default To Here(1);
str = "12/9/2023 19:05:57:754";
res = Word([1 -2], str, ":");
or left with contains to get last ":"
Names Default To Here(1);
str = "12/9/2023 19:05:57:754";
res2 = Left(str, Contains(str, ":", -1) - 1);
-Jarmo