Try the Launcher --> Trainz Settings --> Dev Tab
The setting "Daily backups to keep" will set how many backups are made each day. I think that the automatic timer that set how often (e.g. every 30 min) backup were made was discontinued because it made a noticeable on screen "lag" that people found annoying. The new setting keeps the set number of the most recent backups each day - e.g. set to "3" it will retain the last three backups made on each of the last 3 days (at least that is what my backup folder currently contains)
So if you are heavily into developing a route then you would use a higher number of backups - to recover from a major stuff-up you made last week, for example. If you are just driving routes, then a lower number would be used - to save disk space, for example.
