Hi there, apparently roof bars alone can add up to 15% to your fuel consumption, this is something I read and probably worst case - but the worse case is probably when they are on a small car as they will increase the drag more. If the bars are thule then they can take ages to fit the first time as they require setting up and adjusting but after that it should be a 5 minute job - if unsure ask the supplier to show you. Also, regardless of whether or not you have lockable ones they are easy to pinch and untraceable with a ready value. I always keep mine in the boot or the shed!.
1.75 hours seems a long time for one person let alone 2.
In my experiance after the initial assembaly (10 mins)a two bar set up takes around 10 mins to fit and if you have the short roof adaptor add another 5 mins so there should no reason you cant take the bars off when they are not being used.
Assuming that your roofbars attach to the roof in the same way mine do - there is an alternative approach.
On my Astra, once I'd fitted the roofbars & box (agreed, it's fiddly & time-consuming) I just left the roofbars attached to the roofbox.
To remove it, I just undo & remove the clamps which hold the bars to the roof rails & then lift the bars off the car (2 people job) with the box still on them.
Re-fitting is the reverse of the above (I always loved that phrase in car manuals) & only takes a few minutes to fit & tighten the clamps.
One other tip.
I always carry an Allen key (Hex key) with me & re-tighten those clamps from time to time. Sometimes they seem to work a little loose.
The roof bars are Thule, not sure why it took them so long, it was something to do with the type of bars, they had to order a part in for me. Anyway they were very helpful and the manager really seemed to know what he was talking about. He spent a while with me after the job explaining how to remove the bars and box, what to look out for etc. (he mentioned the re-tightening thing) and he gave me the allen key. I have taken the box off and it's in my garage but I think I will leave the bars on for now. Maybe when the camping season is over (December!) I will remove them. The box is a Karrite Contour 320 which just happens to match the car! I chose this and I was advised it was the easiest to fit, more holes in the bottom. They are a subsidiary of Thule.