Here's my argument for a manual iterative backup feature like the one Somebody is suggesting:
1. It gives you more control over when and why a backup is made. Backups aren't decided by an arbitrary means (in this case, time). This means that you don't have to wait for Construct to decide it's backup time, you can just hit a key and go.
2. It solves the problem of sifting through several .bak#.cap files to find the one you need if you want to revert to a previous version.
I think also that the backup numbering needs an upgrade. Currently it saves as bak1, back2, etc. But when listing these by name in Windows you get this:
I propose that the numbering scheme pads the number with extra 0s, such as bak001, bak002, so that they are listed in the proper order. Perhaps the number of zeros could be taken from the "Number of backups" field in the preferences.
The shortcut key Ctrl-B currently does nothing in Construct, this could create a manual backup. Also, you should be able to create a manual backup without having to turn on the Auto-backup feature.