There are two ways to set due dates on steps within your checklists.
In a Workflow
The first way is by setting relative due dates within the workflow.
In a Checklist
The second way is to set specific due dates in the checklist run while you are working on the checklist. This way is more flexible, but your team will need to remember to set the due dates within the checklist.
This video shows both ways to set and use due dates on steps in your checklists.