Delay on custom domain list status

```ruby
platform = PlatformAPI.connect_oauth(key)
hostnames = heroku.domain.list(app_name).map { |x| x['hostname'] }
platform.domain.create(APP_NAME, 'hostname' => "www.sampleDomain.com") unless

# create domain
hostnames.include? "www.someDomain.com"
=> {"acm_status"=>nil, "app"=>{...}, "cname"=>"www.sampleDomain.com.herokudns.com", "created_at"=>..., "hostname"=>"www.sampleDomain.com", "kind"=>"custom", "status"=>"succeeded", "updated_at"=>....}

# check in the list
platform.domain.list(APP_NAME).map { |x| x['hostname'] }.include? "www.sampleDomain.com"
=> false # any reason?
```

Sometimes, it took about 15 mins+ for the custom domain to be found in list.
Is there a way to tell whether the custom domain will be added to the list?
Can I rely on `domain.list` api? If not, what is the alternative?