Use a modified snapchat APK on Android, or Activator tweak on iOS to reassign the screenshot button to another button.
Has nothing to do with screenshots (which I believe can still be seen from the other side if you reassign button combo).
Say you took a "pause" point on April 25th in the snapchat time machine. Even if you view all your snapchats up to last night, you can still go back to April 25th and view all snapchats from then up to last night again. And repeat the process again later if you so desire.
I don't think this method is as well disclosed as some of the others.
