Azure blob container shared access signature expiring

I'm having trouble with Azure Blobs and Shared Access Signatures when they expire. I need to grant access to a blob for longer than 1 hour (7 days), so I'm using a named container policy, but unfortunately I can't seem to generate new urls once those 7 days are up.

I have the following code to create the "default" policy. Note in this code, I'm setting the expiration to be 1 minute from now, to make it easier to test:

CloudStorageAccount account = new CloudStorageAccount(credentials, true);

CloudBlobClient client = new CloudBlobClient(account.BlobEndpoint, credentials);

CloudBlobContainer container = client.GetContainerReference("files");

SharedAccessPolicy sharedAccessPolicy = new SharedAccessPolicy();
sharedAccessPolicy.Permissions = SharedAccessPermissions.Read;
sharedAccessPolicy.SharedAccessStartTime = DateTime.UtcNow;
sharedAccessPolicy.SharedAccessExpiryTime = DateTime.UtcNow.AddMinutes(1);

BlobContainerPermissions blobContainerPermissions = new BlobContainerPermissions();
blobContainerPermissions.SharedAccessPolicies.Add("default", sharedAccessPolicy);

container.SetPermissions(blobContainerPermissions);

I then create a SharedAccessSignature url with the following:

CloudStorageAccount account = new CloudStorageAccount(credentials, true);

CloudBlobClient client = new CloudBlobClient(account.BlobEndpoint, credentials);

CloudBlobContainer container = client.GetContainerReference("files");

CloudBlob blob = container.GetBlobReference(path);

string sas = blob.GetSharedAccessSignature(new SharedAccessPolicy(), "default");

Console.WriteLine(blob.Uri.AbsoluteUri + sas);

This generates a url, and the url works properly for the next minute (or 7 days in the real code). Once the one minute is over, the url is invalid and no longer works, as expected.

But once that expiration is past, I run the code again to generate a new url. Unfortunately, it generates the same url, which is still invalid.

Are the start/end times for container policies absolute, meaning when I set that policy right now:

sharedAccessPolicy.SharedAccessStartTime = DateTime.UtcNow;
sharedAccessPolicy.SharedAccessExpiryTime = DateTime.UtcNow.AddMinutes(1);

anything using that policy is only valid from 10:10am (EDT) to 10:11am (EDT) today?