Once you have posted your feedback in the Continuous Feedback wall/page, the feedback comments will be available with options to Edit/Delete for the next 15 minutes. After the feedback is published edit/delete is not allowed.
In an unavoidable situation, if you have need to Edit/Delete the post after 15 minutes, please contact your HR admin, who have provision to change the feedback anytime.
PS: Synergita implementation for your Organization may vary from how the features are described here. The screenshots given here may also be different from what you see in your system. Please talk to the concerned person in the Organization for any specific queries.