There seems to be a way to set expiration days in an upload by attaching a Metadata with an "expdays" key to the PutObjectInput but there doesn't appear to be any way to then get this metadata from an object in like a "ListObjects" call. ListObjectOutput returns "Contents" which is a list of s3.Objects but that object doesn't have a metadata field and I don't see any other way to get it either.
The ListObjects calls return a []Object for the actual object list in the result, and Object does not include the expiration. However, GetObject returns GetObjectOutput which does have an Expiration field. So you could iterate your returned Objects and get the expiration for each, though this could be time-consuming if there are many of them.