Although it's a little disconcerting, what you describe is normal when there is a delay between playing the demo and purchasing the full version. Unless you were to completely uninstall the demo and remove the savegame file, the game will pick right back up where you left off, and the real-time engine will continue to operate at whatever game speed was set when the time expired. If the elapsed time is too long, disaster usually strikes.

Arnie's suggestion is a good one, but you'd have to know in advance what would happen when the 60 minutes was up.