In standard workflows, when a delay is added, that delay is relative to the previous action. When an action executes, the next action is scheduled. If that action is a delay, the workflow will wait the specified time before it moves onto the next action.
When adding a delay in a standard workflow, you will set the delay in days, hours, and minutes, and that delay will be relative to when the previous action or enrollment occurred.
In a fixed date or property-based workflow, any delays are relative to the selected fixed date or the date property value set on the contact's record. You will need to decide whether the action will execute on or after the specified date and at what time.
Keep in mind that when a contact is scheduled to execute an action, the workflow does not check for an update to that action -- whether it's a change in the subsequent action (you select a different automated email to be sent) or a change in the length of the delay -- until the original scheduled time arrives. When that time arrives the workflow will check the action to see which email it should send, or if the delay should last even longer.
For best performance and consistency, we recommend you plan and test your workflow before you activate it, and that you not alter the delays or actions once a workflow is live. Learn more about testing and and troubleshooting workflows in the Workflows User Guide.