Ive created a very simple character in Adobe Illustrator, named all the layers, saved it as an .ai file and imported it into After Effects. I then drag the character down to the timeline. I double-clicked the comp to enter the layer so I can use the pan behind too to move the pivot points. Finally I have parented all my layers in correct order.
The trouble starts when I want to animate it. I can't increase the lenght of the timeline. It seems to only go as far as 1 second. Ive tried increasing the composition time lenght and I've tried dragging the layer to extend longer than 1 second but nothing I do seems to work.
You mean the comp which represents your .ai file doesn't stretch any more? You should be able to go into this comp and extend the length of that, and then in the parent comp you'll be able to drag its end point out to make it longer.
If you go to Preferences > Import, then you can set the default length of anything you import to be the length of the composition you're dragging it into (or any other value) so you don't have to bother extending it each time. My guess is that the "00:00:01:00" option is ticked which would make each still image one second long.