Delay between Driver App login and assignment to a Vehicle

When using this API endpoint:
https://api.samsara.com/fleet/vehicles/driver-assignments

How soon after a driver logs in to the Samsara driver application would we expect to see a valid assignment? I understand this will not necessarily be a fixed delay but is the system designed to post these assignments on an event basis off of the login or is there some background process that is not event-driven that is making the assignment periodically?

Is the assignment meant to be close to real-time?

Any insight is appreciated.