[lbriner]

Underground does present challenges but there are many reasons why these seemingly straight-forward jobs take time. You need qualified/certified workers, a load of up-front work related to ventilation, noise, structural movement, surveys etc. Some of this can only be done in engineering hours.

You have issues around the lack of space in central london for work vehicles, the need for removal of rubbish which can't block up emergency staircases, exits.

Then add in the challenges of unknown unknowns and needing to be able to revert any change quickly that can't be done to plan so you don't end up with a closed station and you start to get there.

I assume they had to do them 1 at a time to completion as well?