To add to what ST218 said, levels of certain gametypes take less time to make than others. A single player takes unquestionably the longest time to make because of all the gimmicks, multiple paths, and balancing of difficulty necessary to make a good SP level. Match, on the other hand, is easily the quickest to make, since there are fewer rules to it than any other map. As a matter of fact, my first level, Generic Hill Zone (a match map), was created in less than a week. Granted, it was very simplistic and only used water and special rings as gimmicks, but it turned out nicely, especially for a first map.
Another example of a level that took less than a week to make was Mercury Sea Zone, a CTF level in the OLDC. The first day, I devoted five full hours to building the architecture of the level... the second day, I devoted five full hours to perfecting all of the details about the map.... And then I finished it. Two days? 6.5/10? Not bad, if you ask me.