I'm pretty sure that, in Europe at least, the local church or cathedral would be responsible for keeping the official time, and this would primarily be accomplished through the aid of a sundial. So if the sundial were properly calibrated, the daylight hours would have pretty regular.

I would have to assume that nighttime hours, or daytime hours on cloudy days, were often estimations at best. For the most part, the only folks who really cared what time it was were church officials who needed to determine when it was time to hold daily services. Everyone else would have just listed for the church bells.