If you need a 35-second video to fill 60 seconds, you could use time-stretching or time-remapping.
It's hard to know how to answer your question, because the answers would be different depending on your level of familiarity with After Effects. Until you ask more specific questions, I'm going to presume that you're not familiar with After Effects and suggest that you begin at the beginning.
Thanks a bunch Todd for all the tips. My problem is to get around, all of the layers and three pre rendered video within the project. They are all made for 35 second. I know we can change the key frame for layers, but, how about pre rendered videos?
I'm also very new to AE.
Is it possible to loop the prerendered footage?
As I said, you could use time-stretching or time-remapping to extend the prerendered video.
Please follow the link that I gave to getting-started materials. After Effects is not a program that you can jump into the middle of and try to use by just poking around.