...how long do you think, once it is installed, would it take to remove the front and back sections on a double drop down set up?
It looks like a pretty slick set up, bolting it down on the installed rails. Definitely a two man job however.
I had a quote from an outfitter that included 6hrs of labor to install the ErgoRack, but ended up installing it myself in around 5.5hrs. I felt pretty good about this because I'd spoken with someone else that said it took 2 guys almost 8hrs to install one on their van so I wasn't looking forward to it.
Install actually went really well... it just takes some time to get it all together.
The double drop down system I have has three cross sections (to accommodate different length ladders on each side). The cross sections have a torsion bar that runs through them for the rotating action, so it's not really a simple task to individually remove the cross sections. They would all have to come off together (basically lifting the whole rack off the rails), or you'd have to disassemble most of the rack with the exception of the roof rails that run front to back.
The reality is not everything lines up just perfectly so pulling the entire rack on/off wouldn't really work well. Those two guys I told you about that took 8hrs to install one used this approach. They thought it would be faster to build on the ground and then place the entire rack on the roof in one piece using a fork lift and they had to fight it the whole way.
If you build it piece-by-piece on the roof it's easier to line everything up and get bolts in place before you square things up and tighten the bolts.
The short answer to your question is that once you had some practice, it would probably take a minimum of 2 hrs to disassemble and remove and then another 2hrs to reinstall.