Create a common language between the business and the doers – A call for Agile Scrum

Agile-Scrum tries to do this by breaking down work into stories and then further down into tasks. Each task has an estimated time and the aggregate (SUM) of the tasks is the time for the overall story.

So if someone asks you, "Can you do this by tomorrow?" you should figure out what the stories are and then the tasks. If the work is greater than 24 hours then there's no way.

If the business person can get bought into what the tasks are, or if you have a good scrum master that tracks what the tasks are and the estimated time for each and keeps that data up to date, then communications will be good.

If none of these things are true, you're going to be under water.