I can wholeheartedly recommend
the article on Faerunian Swear Words. I wrote it. It's brilliant.
Also, the FRCS has a section on "Time and seasons". To avoid accusations of cribbing their material, I've made changes where I found what they were saying stupid (e.g. "dawn" is patently the same as "night's end", and sounds less lame) - so I'd suggest paraphrasing as follows:
"Across Faerun, people and monsters both mark time by the rising and setting sun. In southern lands such as Halruaa, there are about twelve hours of day and twelve of night the year round; further north, the days are longer in summer and shorter in winter, with the Dales seeing perhaps 8 hours of daylight in Midwinter and 16 in Midsummer."
"Clocks are both rare and expensive, so hours are not commonly used. Rather, times of day are measured from obvious points: dawn (or night's end), morning, highsun (noon), afternoon, dusk (or sunset), evening, midnight, and moondark (or night's heart). Actual names for these vary widely across the Realms. Only in large cities, where temple bells (particularly of Lathander) sometimes chime the hour, are days divided into smaller units of time; where this happens the hours are referred to by the number of bells, hence "six-bells", "eight-bells", etc., with "twelve-bells" being another term for highsun or noon."
"The Calendar of Harptos is used to mark the passage of the seasons, and is named for the dead wizard who invented it. Each year is composed of 12 months of three tendays (i.e. 30 days). One tenday (or a "ride") is ten days, with the individual days being numbered - first-day, second-day, third-day, and so on. Five special days fall between the months, marking the seasons. The names of the months and the festivals are:
(1) Hammer (January) or "Deepwinter"
-Midwinter festival (January 1st)
(2) Alturiak (February) or "The Claw of Winter"
(3) Ches (March) or "The Claw of the Sunsets"
(4) Tarsakh (April) or "The Claw of the Storms"
-Spring festival "Greengrass"
(5) Mirtul (May) or "The Melting"
(6) Kythorn (June) or "The Time of Flowers"
(7) Flamerule (July) or "Summertide"
-Midsummer festival
(8) Eleasis (August) or "Highsun"
(9) Eleint (September) or "The Fading"
(10) Marpenoth (October) or "Leaffall"
(11) Uktar (November) or "The Rotting"
-The Feast of the Moon
(12) Nightal (December) or "The Drawing Down"
[What would be best would be to have it display details of whichever month & religious festival we were in - but not worth doing special coding for.]
I'll add details of the festivals when I've time.