Usually, the process takes no more than 15 minutes but in some cases can take up to 24 hours.
If the domain is pending for more than 24 hours, it means that the required CNAME record does not exist, or it does not exist for this domain.
In this case, try to do the following steps:
- Use a domain (or subdomain) that is not used anywhere else.
- Add CNAME as written in the instructions. (Appoint tab > Settings > Custom domain)