My team has been trying to switch to Agile recently. The line manager has been taking 1-2 days per user story as a hard limit rather than a guideline, and framing it as a failure of the developer if the time limit is not met. I am not sure if that should be the case since there are a lot of unknowns and possible blockers while implementing a story, or the story might not be broken down properly at the beginning. I think part of it has to do with being stuck in a Waterfall mindset so reviewing and adjusting requirements is not a solution.
What is a good way I can communicate this is causing unnecessary stress? What should I propose as an alternative?