You need to setup a shelf-life for each category.
Go to Categories and alter your categories.
Fill out the shelf-life field with the number of days for your consignment term. A common consignment term is 90 days. Expiration dates are created from the shelf-life days created for each category. This allows you to adjust your term by category.
It's better to setup expiration dates and not use them than to wish you had three months from now. Items that expire don't disappear but they do show on an expiration reports.