Estimating time for planning and technical design using Evidence Based Scheduling

Question

I'm at the beginning of a development project in a large organization.

The Functional Requirements are currently being worked out and documented with our business stakeholders by our Enterprise Design department.

I'm required to produce Technical Design Documents and manage the team to actually build the solution.

I'm wanting to try Evidence Based Scheduling, but as I understand, part of that is breaking the job down into small tasks that are less than 14 hours in duration, which requires me to have already done the Technical Design.

Therefore, can Evidence Based Scheduling only be used after the Technical Design has been done?

How do you then plan and estimate the time it may take to come up with the Technical Design?