With ALDU enabled, upon the next Agent to Server Communication (ASCI), the ALDU event will be generated and the user will be added to the system. By default, McAfee Agent will upload events every 5 minutes. Once the event is sent, generally it will take about a minute for ePO to respond via a special agent wakeup call that the ALDU process is complete. A get user information event is then generated and to request user updated user information including information for the user that was just assigned via ALDU. This again will be sent at a 5 minute interval and ePO will then respond to the client with the user data package.
It is expected that from time of policy enforcement until the Drive Encryption Agent is finished it will take between 15 to 20 minutes. After the system boots, by default, if the machine has not connected to ePO in the past few hours, McAfee Agent will communicate to ePO within the first 10 minutes after booting the system. Assuming ePO has a network connection to the client machine and can perform an agent wakeup call, it will take around 30 minutes from boot up to the time the ALDU user is added.
You are correct that you can speed this up if needed. By clicking Collect and Send Props and sending events when they are generated, the time can be reduced to just 2 or 3 minutes.