Change CNAME to NS records

Hi,
I have a CNAME record in cloudflare pointing to an ALB, e.g: hello.exampleserver.xyz

I plan to delegate hello.exampleserver.xyz so the CNAME record in CloudFlare needs to be changed to NS record. The hello.exampleserver.xyz zone will be delegated to Route53.

On Route53 zone I will have an A Alias pointing to existing ALB.

My understanding this process will require delete and create record.

Are there any potential downtime where hello.exampleserver CNAME record is removed but the NS is not ready yet so Cloudflare DNS will gives NXDOMAIN?

How to test this change and monitoring the changes globally?

Are there any other potential downtime risk doing this change?
Thank you.

So you currently have a CNAME on Cloudflare that points to some external host, and you now want to turn that record into an actual subdomain and delegate it to an external nameserver. Is that correct?

As long as the external services are correctly set up, I’d imagine that should be a relatively smooth transition and Cloudflare should update the records quite swiftly, however there certainly always is the chance of some downtime.

I’d say, simply make sure your external service is supporting the CNAME setup and the NS setup at least for the transition period in parallel. One thing to take into account is DNSSEC, if you have it enabled.