I recently added a timer to my Wanikani via a userscript. I love that is prevents me from getting distracted or thinking too much about a card (6 seconds is my ideal as it makes it so 100 reviews last about 10 minutes give and take your speed and accuracy). It has vastly improved my concentration and speed and has not had a negative effect on my accuracy according to WKStats since I started using it (although I do have it disabled for radicals and individual kanji because I am not that insane (yet)).
I understand that a skipping feature (as in sending a card to be shown later or at the end of the current review session) is already in the works and Iād certainly love if it were possible to choose between a skip and wrong timer (ideally you could customize the time and type of timer for each deck you have).
PS: On the List something called āHave a general review timer that enforces batchesā already exists but Iām too dumb to know what that is so I hope it doesnāt mean precisely what Iām asking for.