Time

We're going to keep track of the days of the year. That way we can keep track of holidays, seasons, character birthdays, moon phases, and all sorts of other nonsense.

Calendar
We need a calendar. With like months and stuff. Donjon has a great tool for creating fantasy calendars. Ideally a year on this world will be the same length as a regular earth year, that way people still have normal ages and stuff.

Watches
Each day can be divided into six watches, each 4 hours long. If you're outside, you can easily tell what the current watch is without a clock or similar device.
 * Twilight (2:00 am - 6:00 am)
 * Morning (6:00 am - 10:00 am)
 * Midday (10:00 am - 2:00 pm)
 * Afternoon (2:00 pm - 6:00 pm)
 * Evening (6:00 pm - 10:00 pm)
 * Midnight (10:00 pm - 2:00 am)