It is impossible to answer how long it will take, as it would be like trying to answer how long is a piece of string?

It won't be hours, that is for sure. A few days might get you going and within a week or two I'd expect to be quite comfortable. That said, I have never worked with Solidworks. People like Eventorizon have, though, and he has been using the software for years. He appears to be able to create pretty much anything in the programme.

I wouldn't ignore Google Sketchup. It is very capable of helping with a first robot. I designed Tormenta 2 completely in Sketchup before building:

http://i1088.photobucket.com/albums/i32 ... 1341527432
http://i1088.photobucket.com/albums/i32 ... 1341527477
http://i1088.photobucket.com/albums/i32 ... 1341527422

As you can see the programme is capable of doing quite a lot. The final robot changed some from the CAD, but it helped hugely. Sketchup took me less than an hour to get used to.