Sounds like they need curves (probability distributions), not point estimates.

+1. I wrote myself a script that does this with distributions based on my personal time tracking data for doing certain tasks.

More concretely, I sample with replacement N times from the empirical distributions of each step, then sum the steps to get N “samples” from the total distribution.

This is called bootstrapping: https://en.m.wikipedia.org/wiki/Bootstrapping_(statistics)

It isn’t too hard to do, and I can confirm that it works reasonably well.

I once tried to give interval range estimates, the manager said "I cannot work with that, give me a single number". (And when I gave a single number, he said "that is much too long" and tried to negotiate it down to 10 times shorter). Happy to be out of there.