@Seapup covered it well. The post you linked refers to the 2x, 4x feature ONLY available for Event Videos uploaded to the cloud and played in the Event Tab Window for videos uploaded with a subscription (including the doorbells). Without a subscription, the Events Tab will only upload thumbnail snapshots.
The -30 \ +30 options, along with manually dragging the timeline, are the only functions to navigate the timeline in SD Playback.
The addition of Fast Forward \ Rewind play speeds into the SD Playback UI is a feature request that is already on the Wishlist with considerable favorable support. Follow the link, vote for it at the top, drop some like 
hearts on posts that you support, and add your post in reply at the bottom.
The Security Camera functionality of the cams is designed to use CamPlus Smart AI Event Videos to initiate Push Notification Alerts to your device. These link directly to that Event Video which will launch the app and play in the Events Tab player. Those cloud videos (and thumbnail snapshots if there is no subscription) are linked to the exact spot on the SD Timeline they occured and a press of the SD Playback Icon Button will launch the SD Playback player qued to the time the event was recorded and uploaded.