You'll be able to view the fields pertaining to Reminders and Expiration only if your System Administrator has unchecked the Use Default Reminders & Expiration checkbox in System Properties. Contact your system administrator if you want to edit the Reminders and Expiration at the Agreement or Quote/Proposal level.
If you can view the fields pertaining to Reminders and Expiration and you leave them blank, the default values that have been set by your System Administrator in the DocuSign account will be used.