There are a lot of different methods of converting strings to datetimes in JMP. Building it from ground up by splitting it from parts is the method which has the highest success rate but there can be easier methods, such as Format Pattern (note that In Format() has << Use Locale argument which you might need sometimes)
Names Default To Here(1);
strs = {"20240207_163752", "20240208_132212", "20240320_180945", "20240321_062705"};
For Each({str}, strs,
datetime = Informat(str, "Format Pattern", "<YYYY><MM><DD>_<hh24><mm><ss>");
Write("\!N", str, " converted to time is ", datetime);
);
20240207_163752 converted to time is 07Feb2024:16:37:52
20240208_132212 converted to time is 08Feb2024:13:22:12
20240320_180945 converted to time is 20Mar2024:18:09:45
20240321_062705 converted to time is 21Mar2024:06:27:05
If using as formula replace str with your column
https://www.jmp.com/support/help/en/18.0/#page/jmp/datetime-functions-and-formats.shtml# - Scripting Guide
https://www.jmp.com/support/help/en/18.0/#page/jmp/date-and-time-functions.shtml#ww2531887 - JSL Syntax Reference
-Jarmo