You absolutely can break up a 25 minute video into shorter lengths and then stitch the comps/video back together without any pre-rendering in a larger comp or render out image sequences which at least means you don’t have to render any videos if AE fails.
At a guess(without seeing the footage) Mocha AE would be the best method for hiding a map on a wall.
Honestly I think there’s going to be pain however you do this.
Please make multiple back ups of your project file. I’m not suggesting anything will happen, but can you imagine you get to minute 24 and the project corrupts?
Sorry I couldn’t give you something more concrete to try.
http://www.YouTube.com/ShiveringCactus – Free FX for amateur films
https://shiveringcactus.wordpress.com/ – FX blog