If all your trying to do is make the footage slower time remap is your tool of choice. Go to Time> layer> enable time remapping, or ALT+CTRL+T (I think) then expand your layer via the swirl down triangle. go to time remap and you should see two keyframes. Now go to Composition settings and change the composition time to the desired length. Now drag the tail of your footage to the end of teh comp, or select your footage hit “end” then hit ctrl+] or alt+] (don’t quite remember) now just drag the second key frame from time remap to the end of your comp and it will stretch out the time. It’s pretty simple once you begin to use it, however time remap can be somewhat intimidating at first.