When you are blessing your pet in the barracks the description mentions the buff will last for 100 turns. When you actually receive the Lights Renewal buff, your pets receive 300 turns of it.

The description from here:

Yea. I was in the middle of tweaking how Blessing worked right up until it was released. I'm still not really satisfied with how it works atm. So I would expect it to further change in some way relatively soon.