Region conversion for
cheats is not a thing. Any region can have data/variables/code in wildly different places even between v1 and v1.1 of a game, never mind an actual region swap.
Sometimes you might find memory sections appear similar between regions (translation tends to only entail translating the text after all rather than messing with variables and behaviours in the game).
The basic naive cheat search approach of get somewhere quiet in the game, start the search, wait for the time to tick down, new search for something that changed (you don't know if it is a timer counting down or counting up), wait, search, wait, search... might work.
However if the existing cheat is controlling whatever element of code is responsible for the timer/its decrease/the eventual oh look time is up goto end of demo screen or the timer itself is wound into the game (often freezing timers can cause events in the game supposed to happen at times not to happen which makes life tricky) then that gets harder and you will want to understand the code that it changes. I don't know what tools we have for the switch to tell you where the binary sits in memory (should be something) as the location of the cheat might tell you there. Length of cheat could mean something (time is likely a short variable, maybe with a pointer, code could well be a lot longer) but also not (if a single instruction needs to be broken for it to work then that might be even shorter than time). You could also view the location specified in the working cheat.
Alternatively. It would not be the first time someone backported a script to a Japanese version of the game. Don't know what it would entail here but could be something.