I'm not sure when this happens, but I noticed that after changing some of my build settings, in particular the clean up strategy and some file patterns in the publish step that the schedule resets to 5 minutes (i have mine set to 15 minutes).
Other things that I may have done are force a build to run and backup the database.
I also tend to open 2 tabs in firefox, one for the configuration I'm working on and one for the dashboard.
Not sure exactly what makes it change back yet...
Ed