The software can perform analyses for any given date/time, so the biggest problem is deciding when to simulate and when not to simulate. Sometimes the client will specify exactly what they require, but mostly they will not. The obvious design days are: mid-summer (21st June) and mid-winter (21st December). These will give maximum and minimum levels of daylight. Another widely-used date half way between, i.e. the 21st of September (you should note that although there are slight differences in the Sun's path before and after the 21st June, for design purposes it is treated as symmetrical - this means that design studies are performed between 21st June and 21st December and the other half of the year is ignored, probably because it is easier to think in terms of June to December rather than December to June).
As well as varying seasonally, daylight also varies daily. East facing spaces will get sunlight in the morning and West facing in the afternoon. The use of Daylight Factors can be useful for reducing the number of simulations (see below). Often you are presenting the worst-case scenario, i.e. the minimum Lux, or the maximum glare.
