Question

If my on-premises account is disabled then how long can I access my cloud account

Answer 1

The answer is 30 seconds.

If my on-premises account is disabled, then I can access my cloud account for 30 seconds. In other words, the cloud account and access to it will get disabled when the next sync takes place through Azure AD Connect. The time between two syncs is 30 seconds. So, you can access your cloud account only during this period.