Hi Rod,
We made it available about a week ago so we can begin testing it with users. There are still some minor issues with it that we continue working on, but it should be mostly functional. If you run into any problems, please post the details of the timeline bugs here with as much detail as possible so we can duplicate it and fix it quickly. We are still working on implementing different playback speeds.
We haven't decided whether this will a be a premium-only feature or not, but we are making available to everyone currently while we debug/test it (to get more testing data).
Also, you can use the timeline for squawk alert flight playback. If you click on the squawk alert box at the top (under the search), there is a new small 'play' icon next to each flight in the popup list. Clicking 'play' will enable the timeline for that flight and isolate only that selected flight. You will see a flight path and an alert overlay showing where the flight squawked the alert. While in this mode, you can click-and-drag the white (hours:minutes) timeline bar section and it will 'scrub' the timeline and move the flight accordingly.