From Space
Icarus is slightly smaller than Earth and has a lesser axial tilt. This means that Icarus has shorter years (320 days), shorter days (22 hours, or 24 'hours' that last 55 minutes) and that it's seasons aren't as extreme when you advance more to the poles. Basically, most of Icarus has a temperate climate.

Icarus has a year of 320 days which is divided into 8 demi-seasons or "months" (early spring, late spring, early/late summer, early/late fall and early/late winter) of 40 days each. Seasons are fairly mild but most places still get snow (or at least sleet) in winter.
Basic time system is determined by the sun and goes as follows:

Early watch: Just before dawn, this is the time most of the people wake up (unless they're fortunate enough to be rich in which case they can sleep in).
Day Break: After Dawn, with the sun roughly 10 degrees above the horizon. For most people on Icarus this is breakfast time, but farmers would already be out on the fields at this hour, while richer people might just be rolling out of bed.
Noontime: With the hours passing and the sun at it's Zenith, people make time for lunch and get out of the midday sun in the hotter seasons. 
After Noon:  
Dark watch: Dusk, with the sun about to go down, most people are getting ready to turn in at this time since there'll be little light to go by until the next daybreak (candles are expensive you know).
After Watch: The sun has now completely set and it's very very dark outside. Every sane person would stay inside since most Knights and Sherrifs are off duty and only a minimal night patrol will be keeping the peace.
Midnight: The time when one day becomes the next. 

When the humans crashlanded on Icarus, they started a new timeline, calling that event the start of year 0. As the settlers organized themselves, paired draks and started making a life for themselves, it is believed that the first castles appeared around 50 years AC (after crash). Sidra Castle was in full swing at around 100 AD, but then fell into ruin, closely followed by De Corvo and Mi'ihen at around 150-180 AD. Currently Icarian timeline is in the early 200's AD.