After giving this some more thought, I realize you're right. We already deal with programs starting on xx:30, now we'd just get used to things starting at x.25, x.50, and x.75. Instead of running from 8:00 to 8:30 PM, a show might run from 8.00 to 8.25.

6 minutes is too much time though, if you tried to fill that with ads you'd lose your audience fast.

Dividing into thirds doesn't really work in a decimal system.