Like Ducky has already stated, sleeving cables is really time consuming.
When I first started doing my PCIe cables from my Be Quiet PSU, I spent over an hour just trying to depin the first bloody cable!!!
The pins on the Be Quiet are a lot stronger than the Akasa 24-pin extension, for the 24-pin it probably took me about 2 1/2 to 3 hours to do the entire thing, it was a doddle to depin this extension.
I'm not to handy with electrics, so the way I did my cables was to remove 1 wire at a time, sleeve it, then stick it back into the plug, and then remove the next one, I've seen people removing all of the wires at the same time, but I know if I were to try this, I'd put them back into the wrong place, even if I did label them!!!
@G-Dubs, I personally think that it would be easier to sleeve a modular PSU that it would a non modular one, at least you can take the cables away from the PSU altogether with modular cables.
Once you've got the hang of it I'd say PCI-E power cable should take 15 mins or so.
What, 15 minutes to do the entire cable?!?!
It was taking me close to 15 minutes to do a single wire!!!