When you manually enroll prospects in a workflow, you can choose to start with the selected step as soon as possible or schedule the start for later.
Open a prospect's panel and click Workflow
OR select the needed prospects > click Manage Prospects > Enroll in workflow.
Choose the needed workflow from the drop-down.
Click Schedule Enrollment and select the needed date and time.
Note: the enrollment date and time are not the sending time of the emails. The emails are sent according to the timing specified in the workflow settings. Read more about the sending time settings.