This tech demo has a script included in it that creates a fully functional day and night system, and a Trade Skill System.
The Day and Night system works by using four maps. The maps are in the order of Day, Sunset, Night, and Morning. The script goes by an on step trigger which increments a variable. Then, when the variable hits a certain number, the map cycles forward to the next map. When it reaches morning, it goes back to the first map. The on step system can be changed to a continuous loop, using ticks to imitate time.
The Trade Skill system can be used to have extra side skills. The way this works is that global variables track experience earned, experience needed to level up, and levels. Whenever a skill is preformed, experience is awarded, and added to the experience variable. The experience needed variable then gets subtracted by the current exp variable, and when the exp needed variable hits 0 or less, it adds on a new level and sets the exp needed higher, and the exp earned back to 0.
The script is moderately easy to follow if your fluent with the O.H.R's plotscripting language.