KPerry
A 'change' could be triggered by a VST with a random element changing value of one of its exposed parameters.

^^^^  Similar to those projects that are automatically "dirtied" even though no intentional changes are made.

Exactly.

Anderton
Set both time and number of edits to 0, which is the default.
 
I use it  based only on time, ....

Thanks Craig.  It never occurred to me that you could "set one" and bypass the other.  duhh 
 
I'm going to try this.
 

I have mine set to 5 minutes and 0 edits.  It sometimes saves after about 5 minutes, but looking at the time stamps it varies a lot.  Interesting that all 10 of the saves I programmed have the same creation time, in every project.  I can't figure out the logic of the time stamps for creation and last modification.