I’m not really used to and don’t really like the 12H format so here is a very little script that will switch them to a 24H format.
The script itself isn’t really nice or optimized, but the job is done.
It seems that they are using react, which load the dom whenever he want so I just added an onload function that will wait for the whole page to be loaded and then execute this script, which mean you will see the 12H format until the page is fully loaded.
I don’t really know react too but it should be possible to use the custom “time” tag and attributes they use.(Hopefully they will add the option to switch to 24H format in Wanikani)
Link of the script : Wanikani Review Forecast 24H Format
HELP! How to install/edit user scripts guide: