For future reference, account-wide items from the Mogstation (such as mounts) often take longer to deliver in-game than single-character items from the Mogstation. At most, it should not take more than an hour after you purchase them.

This delay will also occur with any new characters you make—account-wide mounts will come through to their Mogmail about an hour after creation (and emptying of Mogmail of other items, such as grandfathered Veteran Rewards, and external account-wide DLC, such as OST minions and emotes).