Time is not negotiable.
Many product owners feel they are in a position in which they can negotiate the time it takes to deliver a feature.
Sorry to say, but for a PO, time is not negotiable. Even if you promise and swear you will land a feature on a certain day, you will be bargaining other people’s resources and that is a very irresponsible thing to do.

A product owner — I dare to say — should not negotiate time with stakeholders. This feeds scarcity to the system, to the team, and everybody involved. Things take the time it takes, and that’s it.
A PO, however, can and should — I again dare to say — negotiate scope and priorities. Tasks and work can be partitioned or divided. A scope can be reduced and later polished.
In my journey, I’ve seen many product owners — including myself — trying to negotiate time and it fails every single time, also there’s a catch to it.
At first, the team fails to deliver on time — you take more than what was negotiated, but not more than was estimated — and so everybody has to embrace the cost of broken promises: your team, you, and the stakeholders.
With time, as "experience" kicks in, I’ve seen people negotiate smaller chunks of work and start giving larger estimates. With those changes, they even manage to deliver things on time. Looks great, right? Feels like an improvement.
However, there was still that sense of scarcity that came with a hidden price to it: the stakeholders feel like they can squeeze more things in the sprint. And that’s the catch. The team starts working under more and more pressure and you stop doing the best thing you can do for the project: prioritize.
By prioritizing and scoping - relentlessly - product owners bridge the gap between the unknown-unknowns and a strategic plan. The thing is building a startup product is unpredictable in many many ways and the ability to guide the stakeholders and the team through a sea of uncertainty is core. For a Product Owner, trying to control time is being the captain of a ship and try to control the sea.