This will never be added. Every other SRS program has this basic ““feature”” but wanikani never will, they don’t add any features in general just FYI.
Here’s my post asking the same thing years ago.
I raised this again in a separate thread and even got a direct response from the owner. This is a 1 day change that they would be able to do but simply won’t, their system already knows every review that is due for you that day, they simply need to have logic which makes the ‘start review’ button retrieve all reviews due on the current day. However sadly it won’t be implemented.