I saw a few people saying it might be closer to a month and they were considered alarmist.A couple of days ago "experts" were projecting the fall of Kabul in 90 days. I'd say closer to 9...
Clearly there was a huge failure in terms of assessing the actual facts on the ground. Whether it was overly optimistic about the Afghan government forces (either their ability or willingness to fight) or an underestimation of the Taliban's ability to coordinate and move quickly in a blitz like this - people were clearly wrong.
It was always going to be a shit show, but it seems the speed it unfolded at really has caught people by surprise.