I'm assuming you're using a single client of FileMaker Pro? The gold standard is to use FileMaker Server and its built-in back up scheduling. Preserving the data for 20 years? Interesting constraints...
If it's mostly the data you're concerned about, I'd say a scripted export routine that pushes out a collection of .csv files. I wouldn't trust a .fmp12 file to be usable in 20 years. But a text file would be.
You can script regular FileMaker back up as well.
Save both to a Dropbox folder and a local folder and that should be enough.
How those scripts are triggered depends on your workflow. For example, you can have them run whenever someone opens the file, assuming that file is closed every night, but if you leave the file open for two weeks...then that won't really work.
We are running FileMaker Pro 12 on a Mac and have stored the database file(s) in labeled folders.
I am curious about more frequent backups throughout the day.
Is Time Machine (Mac back up) a good solution for making incremental backups throughout the day? Or is there something else we should consider?
You are skating on thin ice. FMPro client is not really a robust multi-user server and Time Machine is not really the best option for your backups.
I suggest that you exclude the FMPro folders from your TimeMachine backup preferences. Use Calendar and Applescripts instead.
Use Calendar to set up a scheduled task which runs every hour. A calendar schedule can call an automator script or an applescript. The applescript then calls a filemaker pro script which does a Save a Copy into your Cloud backup folder. The advantage of this is that the task scheduling is handled by FMP. If it’s busy when the applescript runs, the applescript has to wait.
For long term storage of your data I agree with David Jondreau, export the data from each table as a csv. Obviously this sort of archival storage only needs to take place at significant intervals, daily? weekly? at project close?