A writer's life is not bound by the same work conventions as others...it's not a M-F job unless you're one of the very unusual, perfectly organized writers (I know one or two. I am in awe, but I don' t have time to be in awe very long, so...moving on...) Depending on deadlines, illnesses, etc, etc., etc., most of us seem to work very long hours and every day of the week...or close to it.
So not realizing it's Saturday already is normal. Unless I have an event scheduled, Monday-through-Saturday is all the same, dawn (or before) to midnight (or a little after.) Not all sitting at the keyboard (sometimes, but not always)...there's cooking, laundry, cleaning, shopping, and the business side of writing (correspondence, phone calls, etc.) If I'm not sick (or too far behind on a book) Wednesday evenings and Sundays are taken up with choir. Sometimes, when we have a big performance coming up, that includes some other rehearsals as well.