We don'z know anything about the specific template, its keyframes and whatnot. Simply stretching out the project most definitely won't be enough...
You're talking about slowing it down by a factor of three. That is a whole flippin' lot. My advice: if you don't know After Effects already -- and there's a deadline associated with this project -- go to Plan B.
Or come up with a Plan B.
Because by the time you're able to wrap your head sufficiently around the way AE works AND you have all the template intracacies figured out, you probably willhave missed the deadline.
You can simply slow thew whole comp down to the required length, but as the guys above have mentioned, this will simply be a very slow slow mo. Depending on your content, that may be okay, or it may be unbearable to watch. Up to you, but here's the process if you want to try:
In the Project Window, drag the main 20 second composition to the New Composition icon. This will create a new composition that has the original composition nested in it.
Change the duration of the new composition to 1 minute (or whatever you want).
Select the nested comp layer in the new comp. Then choose Layer/Time/Time Stretch. Type the desired duration into the New Duration box - in your case, 01:00:00 - one minute.
Thanks for the assistance guys will look into all options and take them to the production manager, thanks again for all your help