Too Much Happiness Decreases Happiness?

[MsMagick Resident]

The solid circle is your indicator that they currently have the benefit of gaining love faster - regardless of whether it is from milk or cuddles - and, for cuddling, it is determined according to when they were cuddled. Kitten Longmeadow has discussed it at multiple Q&As, but I have never gotten it pinned down exactly re: things like how the clock runs when you do overlapping cuddles.

Basically just know that 1) if the happiness circle is solid, they are gaining love at the increased rate, and 2) they need at least 30 minutes of cuddling every 24 hours to get the benefit.

When the benefit wears off, the circle is no longer filled in. It does get filled in almost as soon as you pick them up again, so you obviously don't have to hold them 30 minutes before the 24 hour clock starts ticking. Therefore, it's probably not a bad idea to go a little over 30 minutes from the time you picked the last one up so you get some overlap time, but you don't need to cuddle them for hours - or get up all wrapped up in watching their minute-to-minute happiness (unless they are otherwise ready to breed).

The formula for the happiness percentage seems to be fairly complex, but it is not tied to whether the circle is solid and it's isn't really a factor in how fast they gain love - only in whether they are ready to breed.