There are six days in a month in Book of Hours (unless the month is Numa). The months are indicated by a scrolling display of four branches/twigs, one for each season.


At the start of...
...day 1, the tips of the preceding twig are still visible: six full days till next month.
...day 2, the tips of the current twig have reached the left side of the calendar. 5 days left.
...day 3, the second branching of the twig is almost off the left side. 4 days left
...day 4, the top curve of the twig is nearly half offscreen. halfway through the month!
...day 5, the third branching of the twig is almost off the left side. 2 days left.
...day 6, the bottom curve of the twig is nearly half offscreen. 1 day left.
When only the rightmost tip of the twig is visible, the month it represents just ended.

And I have included a graphic! Okay, that's the end of the guide. Seeya.