By understanding my previous posts:

• Hybrid Azure AD Join – How a computer device is recognized as Hybrid device ?
• Azure AD Connect: How to manually synchronize using import, syncronize, export?

Now it is easy to find out how to make hybrid join happen immediately:

1. Setup the hybrid AAD auto join infrastructure, i.e. AAD, SCP configuration, rollout plan (by GPO), etc.
2. Make sure the userCertificate attribute of the computer object existing.
3. Delta import from on-premise AD (run Delta Import on the on-premise AD connector)
4. Delta synchronize on the on-premise AD connector (run Delta Synchronization on the on-premise AD connector)
5. Export to AAD (run Export on AAD connector)

About Error: AAD Cloud AP plugin call Plugin initialize returned error: 0xC00484B2

This error also appears, even after the device is hybrid AAD joined. So you should not rely on this message to trouble shoot your auto hybrid AAD join.

References:

[1] How to configure hybrid Azure Active Directory joined devices