You can manipulate that buffer as much as you want - rewind, pause or fast forward - and you can also use Flashback Recording.
Just rewind the video to where you want to start recording, and press the Record button. Elgato Game Capture HD will start recording from that point, even if it's from an hour ago.
Here is an example of how you can use Flashback Recording with Elgato Game Capture HD:
1) Rewind to a previous point. In this example, rewind 10 minutes.
2) Press the red Record button. Elgato Game Capture HD will record those 10 minutes, and then jump to Live.
3) Wait 10 more minutes. You will see Live video during this time.
4) Press the button again to stop recording
5) You will now have a file that's 20 minutes long.