Delay steps can be inserted at any stage of your workflow execution, they can happen after or before any action. The workflow execution will be halted for the given amount of time and then resumed to the next step in the flow.The action can also be skipped using the skip parameter conditionally to allow more complex usecases of when to wait and when to send an email immediately.
Changing the step content after triggering the workflow with delay step will not affect the existing pending delayed notification content.