When to water a lithops while dismissing any and all fears of it being over watered ..... NEVER

Yeah definitely follow the "when in doubt, don't" motto for this one.
Some of these specimen can go the whole year without watering, of course that's not recommended either. But it definitely sounds like you're watering them way too often. During the summer they're not growing, you should water them every two weeks or so, depending on your weather condition, and if grown indoor/outdoor. Usually they will look a bit shriveled when they're thirsty, if they look plump and hard when touched, they are doing just fine. After they flowered you should stop watering for the whole winter as they start to grow new leaves and it takes the moisture from the old leaves. Once the old leaves shriveled and dies away then you can begin watering again, but VERY sparingly.

And no they don't need fertilizers EVER. They need to be in very lean substrate.

I just started growing these, and from what I've read here and everywhere else that's how to do it, so yeah go ahead and try to ignore these things, and they'll do well!