Labeling with correct day

I’ve been using this app on & off for several years now. It always puzzled me as to why when, for example, I wake up on Sunday morning, the app has identified the previous night’s sleep as “Sunday” when it was clearly Saturday night. I’ve looked in the settings, have played around with the one that seems like it should control this (changing cutoff from 12 to 24 and back) but nothing changes. Would love to know how to make this change.