First off, this is not like many of the other games out there on computers - most games are meant to be quick, or relatively quick - and then the game is over, or there is little left to do - FoE is a game designed to be played over a very long period of time. Which is a nice change of pace from all those other games that are designed to be finished in hours/days/weeks or months. Sure, some of those other games have expansions as well, but again, designed to be quickly completed. FoE is doing quite well with their different methodology.
Some productions can be completed on different timers, but the most common timer is the 24 hour completion - which most Great Buildings, Event Buildings and other activities (such as aiding and tavern visits) are used. FoE is a game that is able to be played in pleasure time, a little bit of time each day (play more if a user wants, but it is a slow and leisurely paced game). There are some exceptions, such as GbG, which can be played multiple times a day, or near constantly - but the main basis of the game - your buildings, are kept to the regular daily. Unforunately, this type of style does lead to time creep as well - but that is up to the individual player.