The pet food "issue" isn't really one about duration as I see it.
Even if buffs lasted 100% longer I'd still never use my own pet food on most buildings, which makes their ability kinda useless.
So, can we somehow use a Keeper to buff a building
without the use of pet food? Perhaps an interface on the "collect tab" where you can click to use?
In this case, the keeper used could be
1. unavailable for the duration of the buff it gives: 2.4h (10% of the feeding effect which is 24h for this pet)
2. unavailable until you collect from this building (4h11m in the example, but can be from 0-48h)
3. unavailable for a standard duration (literally any time interval deemed fair/balanced)
There should, of course, be a diamond option as well so inno can get something out of it aside from the diamond cost to upgrade your Keeper's Hut.