In Task view, if you have the timebox sidebar visible and use the left/right arrows to navigate to a day other than "today" and then click the "Focus" button next to today's date the "focus" screen will show the day that the timebox was viewing.

I'm classifying this as a bug since you would intuitively expect when you click the "Focus' button next to todays date that the focus screen will show today's tasks and not whatever arbitrary date you were viewing in the timebox sidebar.