Several thoughts went through my head before I realized what's wrong:
1. I guess longer caching means more stale data, which is why it's a downgrade?
2. Maybe this isn't the TTL I thought it was?
3. Maybe this isn't the cache I thought?
Then I clicked on the link and realized I had been mislead my the title.
The SI symbol for minutes is "min", not "M".
A compromise would be to use the OP notation "m".