Usually it's a matter of a few hours before your domain get active, but it can take anywhere between 10 mins to 72 hours. Why? When you add a domain to your account there is a lot that goes behind such as the following:

• DNS propagation can take anywhere between a couple minutes to 72 hours. Until then we can't proceed with the following steps.
• Once your domain is pointing to our IP, we can now start provisionning a SSL certificate for your domain. You can always expedite this step and shorten the wait time by using CloudFlare as your DNS provider and activate their Universal SSL in flexible mode.
• After the first two steps are completed, we audit and release your domain as Active to your account.