When in Central Console model, it is observed that the status of agents takes long elapsed time (in terms of 20mins to a few hours) to update to "Start Virtual Users". It appears that only one agent has reached the 'Starting Virtual User" when it is expected for the virtual users to start all at the same time.
Product defect. The bfp file is rather large, and requires to be transferred to each agent machine to start the virtual users.
Run separate console.