The fundamental problem remains: it’s difficult to predict how long it will take to solve a series of puzzles. I worked in a dev group where we’d take the happy path estimate and double it… it didn’t help much. So often I’d think something would take me a week, so two walls was allotted, but I made a discovery in my first like hour/day whatever that reduced the dev time to like a couple days. Then, there were tasks that I thought I’d solve in a few days that took me weeks because I couldn’t foresee some series of problems to overcome. Taking a guess and adding time to it just shifts the endpoint of the guess. That didn’t help us much.

You assume that PMs will just accept whatever estimate you give and not just say 2 weeks from the off and refuse to budge.