This is a complicated topic.

You could use AirflowNetwork for this, and use an EnergyManagementSystem:Sensor to connect it to your schedule, computing an average velocity (m/s) from the airflow rates (m3/s) in/out of the Zone. See Air velocity in Airflow-network.

This is going to be perhaps rough though, AirflowNetwork doesn't calculate velocity, just mass/volume air flow rates.

Another solution (the right tool for the job actually...) is to create a CFD model to calculate air velocity around where occupants are supposed to be, and import that back into E+ as a schedule, but that isn't trivial, and it could be way overkill for your needs too.

This other question How is air movement modeled in EnergyPlus and what are typical values? should be of interest too.