Manager: We (meaning you) need to do task A. How long will it take?
Me: Task A will take X days to do.
Manager: That seems awful long.
Me: How long do you think it should take?
Manager: It surely could not take any longer than Y days.
Me: Ok, it seems you have an answer to your question then.
Later:
Manager: It’s been Y days, why isn’t task A done yet?
Nothing is more triggering to me than the question “how long will this take?”
It will take as long as it fucking takes, and you shouldn’t be reporting anything until it’s done. Measure progress by fully working, end-to-end features, not by a number of hours someone pulled out of their asses.
You need to allocate resources and prioritize tasks
If task A takes a day then it might be worth doing. But if it takes 2 weeks then maybe not
You can estimate roughly if you know the scope amd constraints.
And you can’t plan if you don’t have rough estimates (not counting OPs example)