When a requirement is sent for review, a requirement owner can add a date for which they request the reviewer's to provide their response. In the details window of the desired requirement, click on to expand the Reviewers tab. If there is at least one reviewer, there will be text above their names reading Click here to request the review by a certain date. When the text is clicked a calendar will appear and a date can be selected.
Users will need to be the requirement owner, and have project permissions to view and edit the requirement to perform this action.