It no longer matters if you've represented another country or not - the minimum wait after a change in citizenship is now 2 years, and 3 if you have represented another country. Before, the Gulf States would simply go to the Kenyan trials and snatch up the fastest guys who'd never run for Kenya, give them citizenship, and boom - instant team. This new rule is in response to that.
As for the timeline, it can take far less than 5 years to get a green card. My wife's took 18 months, and that was after doctor screwed up something on her exam form - had that not happened it would've taken about 8 months. Once she had her green card, it was a 3 year wait before she could become a citizen. We filed that paperwork in June 2010, and she took her oath in November, so it was only about 5 months on that.
We've certainly heard horror stories from other people, but her process was very straightforward. We didn't even use an attorney, just filled out the papers and sent them in.