Time

The calender in-game is basically the Forgotten Realms Calender.

The Hours of the Day

The day is 24 hours long, broken up by the rising and setting sun. Most people break up the day into large slices - dawn, morning, highsun (noon), afternoon, dusk, sunset, evening, midnight, moondark (night's heart), and night's end. These are of neccessity not exact, and there is often confusion fro travelers in foreign lands.

In large cities, temple bells toll to mark the hours, and each hour is a "bell" - counting from the hour after midnight or noon and numbering 1-12. Noon and midnight are both referred to as "12 bells," though some of the temples most concerned with precise time (Gond and Lathander, for example), have gone to a 24-bell nomenclature, where noon is 12 bells and midnight is 24 bells.

The Faerunian Year

The Calendar defines the year for most of Faerun. It defines a 365-day year divided into 12 months of 30 days - or 3 tendays - each. Five special days fall between the months, and every four years a leap day, Shieldmeet, is added to the calendar immediately following Midsummer night.A tenday is also, though less commonly, called a ride, and consists of ten days. The days do not have names, but are instead referred to by number: first-day, second-day, and so on. Most people count using their thumbs as first-day; halflings, however, are famous for using their pinkies to count first-day, and thus the phrase "counting like a halfling" has come to mean someone is being different just to be difficult.
The months and holidays are listed below; the days of the solstices and equinoxes are:

• Winter Solstice: Nightal 20
• Spring Equinox: Ches 19
• Summer Solstice: Kythorn 20
• Autumn Equinox: Eleint 21

The Calendar

Month	Name	Common Name
1	Hammer	Deepwinter
Annual holiday: Midwinter
2	Alturiak	The Claw of Winter
3	Ches	The Claw of the Sunsets
4	Tarsakh	The Claw of the Storms
Annual holiday: Greengrass
5	Mirtul	The Melting
6	Kythorn	The Time of Flowers
7	Flamerule	Summertide
Annual holiday: Midsummer
8	Eleasis	Highsun
9	Eleint	The Fading
Annual holiday: Highharvestide
10	Marpenoth	Leaffall
11	Uktar	The Rotting
Annual holiday: The Feast of the Moon
12	Nightal	The Drawing Down

most of this information has been taken from here:  look at the expanded calender:

http://dnd.steinhour.net/Forgotten_Realms_campaign/Forgotten_Realms/DnD_FR_calendar.html