Daily 'apt-get update' slowness when using ec2 mirror us-east-1.ec2.archive.ubuntu.com

For the last week or so, I've been experiencing a nightly ~1-hour span of time (starting around 11:30 PM PDT), where 'apt-get update' hangs for as long as 30 minutes on systems configured to use the Canonical ec2 mirror in us-east-1:

http://us-east-1.ec2.archive.ubuntu.com/ubuntu/

While that behavior is occurring, the same slow response time seems to exist both for requests from EC2 instances and also from non-Amazon hosts (my home Inet connection, at least).

Navigating the mirror from a web browser becomes noticeably slow in addition to the impact on apt-get.

It looks like similar behavior has occurred with other ec2 mirrors in the past; one suggestion I noticed (http://www.thomasvjames.com/2015/03/ubuntu-apt-slow/) involves forcing the use of an S3-backed apt mirror by appending .s3.amazonaws.com to the repo URL.

However, while the bucket at http://us-east-1.ec2.archive.ubuntu.com.s3.amazonaws.com seems to exist, I get 403 Forbidden errors if I attempt to use that URL in my sources.list and re-run 'apt-get update'.

Someone pointed me to this announcement from 2012 that all ec2 repos were now s3-hosted by default; does that mean that using the .s3.amazonaws.com URLs is moot? Or was the change to use s3 to host us-east-1.ec2.archive.ubuntu.com rolled back at some point?

https://lists.ubuntu.com/archives/ubuntu-cloud-announce/2012-July/000029.html

Thanks!