I built a short (10 foot) one that didn't provide enough cooling power. So I built a 20 footer. The first one took me about 2 hours to build, while the second one took about 30 minutes.
I don't use a pump for my wort - just let gravity pull it out, which provides a nice slow flow. I use a harbor freight cheapo submersible pump in a 5 gallon bucket with ice to recirculate the cooling water. When it gets too warm, I pause, dump the warm water and add cool water with some more ice.
It takes me about 20 minutes to chill the 6.5 gallons of wort from boiling to about 55 degrees. My immersion chiller took about 45 minutes, and I think my cold break wasn't as good. However, it still definitely worked!
On my first build, I was going to do the wire turbulent thing. I had a VERY had time trying to push the copper with the wire on it through my hose. I gave up after about fifteen minutes of pushing, sweating and swearing. In practice and at the small scale where we are, I'm not sure the turbulence really matters. My wort gets darned cold darned quick.