In the 10s, that number dramatically increased to 918 days.

This is what I was told by a coworker who had been in the semiconductor industry for decades (can't ask him for sources now because he's dead):
During the Obama administration, they set up a tax cut to incentivize companies to build more factories, where you would get a tax break if you filed plans within a certain time frame, but you only needed to build one building to take advantage of it on the planned future construction. As an example, Intel slowly built a new fab in Arizona, and, once it was completed, they left it empty for years, only starting to install equipment in 2019. This facility was also built with the move to 450mm wafers in mind, so it was much larger than previous fabs. The move to 450mm wafers never happened, and probably never will.

A big part of the speed is the extremely poor mid to long term planning. Constant rework because of constantly changing demands, slashing workforces during slow periods and then struggling to fill positions long after they should have been filled, and more bullshit as you can imagine.