When off work for several weeks after an operation last year, I decided to build-up a TT bike as 'a project'.
I fancied the idea of 'building my own bike' and it would be something to do with all the time I had on my hands.
I bought the frame and all the bits on
eBay over several weeks, as I could be patient and wait for decent prices.
When eventually I had everything, I screwed it together and hit a major anti-climax : it was far, far quicker and easier than I'd anticipated !
Even with lots of take-it-slowly, working-out how things go together, playing around and experimenting, it took less than an afternoon to assemble the basic bike, plus the following morning to cable it and fit the bartape, etc. - the stuff where there's a choice of just shoving it on quickly or taking time to do very neatly and precisely.
I think if I were to do it again, now understanding how to do it, it would take me only 2 or 3 hours...
I'd kind of imagined it as a project like building a kit car, but it was far simpler, easier and quicker than that so I was left a bit disappointed.
I've seen bike shops charging £20 or £30 to assemble a bike, presumably they can do it in an hour or two.