Just look at it in all its ugly syntax, this is Old School, pocket protector wearer stuff:
for /F "tokens=1-4 delims=/ " %%i IN ('date /t') DO (
doSomething.exe > "%DT_YYYY%_%DT_MM%_%DT_DD%.txt"
UGLY. Where in the hell does the j,k, & l come from? Some sort of crazy auto-magicness? This is from the times when it was best not to question how it works. I still don't know but at least I got this trick card in the deck now.