Estimates are difficult for developers and product owners

The last director I had would ask "is it a day, a week, a month, or a year" he understood that's about as granular as it's possible to be.

And he really only used them in comparison to estimates for other tasks, not to set hard deadlines for anything.

This is essentially t-shirt sizing without all the baggage that comes from time. Your boss is trying to use the relative magnitude but it's inevitable that people will (at least internally) do math like "7 day tasks is the same as one week task", or worse over-rotate on the precision you get from day/week/month, or even worse immediately map to the calendar. Suggestion: don't use time.

Knowing nothing else about him, I like him based on this alone.

I've been in planning sessions where someone would confidently declare something would take half a day, was surprised when I suggested that it would take longer then that since they were basically saying "this'll be finished mid-afternoon today"...and was still working on it like 3 weeks later.

If you pretend not to use time, everyone will do an implicit time mapping in their head anyway. I've never seen it go any other way.

Besides the usual unknown unknowns, I've also seen this happen with tasks that involve a lot of coordination in the SDLC. Oh the PR went up at at 2pm PST? Coworkers in EST won't review it until tomorrow. Maybe some back and forth = another day until it clears review. Then QA happens. QA is heavily manual and takes a few hours, maybe with some false starts and handholding from engineering. Another day passes. Before you know it the ticket that took an hour of programming has taken a week to reach production.

Surprisingly prob yes

But still we are much better at estimating complexity

Time estimations usually tends to be overly optimistic. I don’t know why. Maybe the desire to please the PO. Or the fact that we never seem to take into account factors such as having a bad day, interruptions, context switch.

T-shirt sizes or even story points are way more effective.

The PO can later translate it to time after the team reaches certain velocity.

I have been developing software for over twenty years, I still suck at giving time estimates.

Here's my observation: ballparking an estimate for a whole project, in my experience, tends to be more accurate than estimating each task and adding them together.

I like to think of this as 'pragmatic agile': for sure break it down into tasks in a backlog, but don't get hung up on planning it out to the Nth degree because then that becomes more waterfall and you start to lose agility.

Time estimations, or conversations to days or other units, typically fail because if a developer says 1 day they might mean 8 focused uninterrupted development hours while someone else hears 1 calendar day so it can be done by tomorrow, regardless of if a developer spends 8 or 16 hours on it.

As mentioned in a sibling comment reply:

Time estimations, or conversations to days or other units, typically fail because if a developer says 1 day they might mean 8 focused uninterrupted development hours while someone else hears 1 calendar day so it can be done by tomorrow, regardless of if a developer spends 8 or 16 hours on it.

Are we estimating developer cost (investment cost, writing code only tome), development costs (investment costs including QA time), or time to delivery and first use? People want and use estimates for different purposes. You point out great reasons why knowing what the estimates are for is important.

That's true. Anyplace I've worked where we did planning poker, "points" were always just a proxy for time.

It's probably not possible to fully prevent people from thinking about time at all, but the more friction you can add, the better.