By using my mind to reason about how long the task(s) will take, based on past experience of using the tools, processes and mental frameworks to achieve similar task(s) in the past? Has Claude really totally preempted even such critical thinking abilities?

> I can estimate how long it would take me to do something but Claude?

If I were in this situation, what I'd do is to continue to give estimates as I always have before, ignoring the use of genAI, and keep track of how much the accuracy of those predictions have changed. That would give me some real data on which I can begin to adjust my time predictions.

To do it any other way is to just be guessing blindly.

Depends, do you want to give an honest answer? Do you have a stake in your employer succeeding?