I have connected my site to google+/youtube... G+ gave me the custom option last week, so it has been at least a week, and I still do not see the custom url option for youtube. I read one post that says once you setup your custom url on G+ then that is the same url you will use for youtube, however, i see no evidence of that.
Custom URL for channels that meet the eligibility requirements will be able to claim a custom URL based on channel description, Google identity, associated website, and a few other factors. This is to ensure that channels can get a URL that is unique to the channel brand, consistent on YouTube, and shared across all of Google’s services.
Have you met the eligibility requirements and checked off every step here? https://support.google.com/youtube/answer/2657968?hl=en
Hi, change your personal profile in Google+ and their you will find "Scroll down to Link". Follow the promts to create your URL and , finally to verify your change)