Quote from Hyakkidouran on February 5, 2008, 9:35 am

I personnally learned enough to do my first basic chamber in about a week. You can find this map there : aperture-secondary-labs-room-1-t739.html

It gives you a good idea of what can be done in that much time.

But you have to note that that I used CP4P (common prefabs for portal), which contains premade elements such as buttons.
But I advise you to try to create at least one of these elements first yourself to get familiar with the input/output concept.

Also I made some 3D theory at computer school, which help a lot to understand some concepts quicker (especially the texture application made sense almost instantly to me, but all those numbers can be confusing if you don't know anything about 3D.)

So it took me a little more than a week, but I wasn't a complete newbie with 3D (even if I almost never did any modelling, only theory to render textured cubes in an engine :p)

I think that if you are quite good in math and motivated enough to spend most of your free time reading documentation, it is possible to learn enough to do an already pretty cool map in about 2 weeks, by starting with no knowledge about it.

Following the good advices of veterans from this forum is definitely a good idea, too. They are very helpful and can give the solutions to your problems very quickly if you ask nicely.