What’s the error message you get? I think I know what the error will say, and that will be your first clue. Posting this info might also help you to get help…
Anyhow, to achieve what Richard has done, open up the graph editor’s properties panel (n-key) and scroll down to the bottom. There is probably a generator modifier on that channel, it generates a 1:1 curve. That is a curve that is a straight line moving the same amounts on the x-axis as the y-axis, x = 5, y = 5. Blender adds this in on certain channels by default, like your evaluation time, and it’s also why your are probably getting an error message. So remove the modifier and the curve is gone. You should now be able to key frame the evaluation time, if that’s what you want to do.
You can also create your own custom curves in the graph editor. After the generator modifier is removed, move your mouse to some point on the grid and ctrl-LMB to insert a point, or key frame. Repeat for 2nd key. It’s not a very precise way of creating keys, you can’t be sure exactly where you are at on the gird, unless you really zoom in on the view, but even then, not precise. So once you add a key this way, look to the top of the properties panel, the key’s location is a numeric field that you can enter data into. Likewise, if your using bezier curves, the location of the handles is there as well.