How long does it take for you to finish a skin?

It took me 3 days to make one.

What about yours?

Any tips on making skins faster?

Depends on skin difficulty and quality you're trying to achieve. I'm quite slow as I pay big attention to details and I push every pixel correct,so fairly basic skins need an hour or 2,something more difficult like this one asked me few days with few hours of work in each.

nice looking skin you made there! how many skin you've made? when was the time you started skinning?

Depending on the skin (and the car I suppose, some are easier than others), I can spend anything from 30mins to a few hours spread over a few days.

If you are using the game to preview your skin, use the CMX viewer instead...this will save a bit of time.

Edit: You will get faster with more practice certainly, you start to learn where things wrap and can get it very close on the first attempt for one thing.