When does Amplify stop trying to verify a custom domain?

Amplify Hosting checks for DNS records for pending domain until 48 hrs. Although, it is important to update your CNAME records as soon as you create your custom domain. After your app is created in the Amplify console, your CNAME record is checked every few minutes to determine if it resolves. If it doesn’t resolve after an hour, the check is made every few hours, which can lead to a delay in your domain being ready to use.

Reference - Troubleshooting custom domains