What everybody keeps forgetting over and over again is that software is super complicated even if it can be changed from a keyboard without the use of physical morphing tools.
People who do not themselves generate software are in the position of telling the people who generate software how to do it and what the constraints should be on the outcomes.
Accept that it is complicated and that you cannot know in advance when it will be done unless it is a super simple request.
It is indeed more like oil field exploration than it is like sweeping the floor.
You cannot really know where the solution to a complicated problem lies in advance and therefore you cannot predict how long it will take you to find it.
People on the finance side just need to face the fact that there is risk that cannot be eliminated in advance or even quantified particularly accurately.
If your investors cannot stomach this, they probably need to invest in something other than software development.
Good luck with finding that in 2026.