I'm glad you pointed out the fact that different maps will take greatly different amounts of time. The most I've ever spent making a map which is currently finished was 6-12 months. So far I've had two maps which took me that long. Some of the maps I currently have in production have already taken me well over a year and still aren't near completion. One map took me about an hour to make just because I wanted to take a break, and some took me under two days. On average, it takes me about 1-2 weeks to make a really exceptional map though.
I'm not sure if you include storyboards and the rest of the written stuff you sometimes do before/while making a map, but if you are, that time frame can go way up. Time Shifter took me about a month straight to make, and a good week of that was simply making a storyboard/event timeline/plot/whatever you want to call it. I had a stack of about 30 papers completely filled in before I finally finished the completed timeline. One of the maps I'm currently working on runs on an extremely complicated randomized pattern system which I'm creating every part of on paper first. I have 20 pages for that already, and have only finished one part of the pattern so far.
True story related to this. I was working on an RPG (which still hasn't been finished yet) and after days of working on mind-numbingly tedious triggers, I decided I needed to take a break, and an idea came to me about being in a spaceship and trying to stop aliens from entering the ship and killing you. It only took a few minutes to further elaborate on that idea, and come up with aliens forcing themselves onto the ship after its power had died. Thus was born Deadship. The map only took me a few hours to make, and I went on bnet to take my much needed break by playing this new map. Lo and behold, people loved it. I got so much positive feedback from that map, and such high demand for an updated one that quite a few people made completely original versions with the same theme and 'Deadship' in the title, that I made an official newer one with space terrain, and painstakingly duplicated the terrain exactly (why I didn't use space in the first place is a mystery to me). After adding all the new features, the updated version took me about two months (I put the people's names in the briefing who 'harassed' me the most into making it -_- lmao). I was really surprised to get such a massive wave of positive reaction to something I quickly threw together just to keep myself sane.