How to disable the "Your computer time is almost up." dialog?
/System/Library/CoreServices/SecurityAgentPlugins/FamilyControls.bundle/Contents/Resources/English.lproj/FamilyControls.nib is a binary XML file that can be opened by TextWrangler or other text editors. This isn't a developed solution (yet), but I'd suggest some well-placed edits to this nib might be able to disable the dialog, perhaps by making buttons disappear. At any rate, this sounds more promising than randomly zeroing out portions of the binary using a hex-editor, which is the other channel I've been exploring.