"Dynamic calendar icon" installs a script that checks how much time is left until midnight, then waits until then, updates the icon, and repeats. The problem with this is that it breaks if the time zone changes. Suppose you set your phone to flight mode, then board a plane and fly two zones to the east. If you arrive at 0030h in the destination time zone and disable flight mode, the icon won't update until 0200h.

This implementation instead uses the N9's built-in task scheduler (timed), which is aware of time zones and can be set to immediately run my program on time changes - so it's always in sync. Also, since timed is already installed and running in the first place, Calendarrr uses no additional resources.