Overheard on Twitter
The Start of a Project Is the Worst Time to Estimate Its Duration or Cost
This is only the case if those you've hired know nothing about what capabilities are needed to produce value the project, what Features are needed to produce that Value, when those Value-producing Features are needed to meet the time cost of value payback process, what risks there are for meeting those value producing outcomes, and how the work effort to produce that value are to be measured (physical percent complete) to increase the probability of success for your project. As the project progresses this understanding will, of course, improve with feedback, working product, and learning.
If those you've hired don't have some sense of these needs, to some level of confidence, you've hired the wrong people.
From Estimatiing and Reporting Agile Projects with the SRDR