Well, I stopped feeding Jazz 3X a day before she was 6 months....3 or 4 months maybe, and she's done just fine. Her interest for that midday meal had dropped a bit, so I took that as my cue that it was time to cut it back.
I don't think there's anything wrong with a dog's appetite fluctuating somewhat. Mine does. I'm sure yours does too. I think changes from day to day are normal. What you're looking for is enough consistency of change to form a pattern.
I try and look at it like this: Over a period of a week to 10 days, are my dogs getting what they need, and are they eating their required amount of food....more or less? Day to day, it may go up or down, but over a longer period, is it averaging out? If that's the case, and most always it is, then I just leave it alone, chalking it up to normal fluctuations. As Jazz is still growing, and over time has required a bit more food, just not as often, when she started cleaning her bowl and seemed to be frantically looking for more, and that behavior continued for a week or so, I upped her portion marginally, because it was obvious from that consistent behavior that she required more. She's always done that though, from time to time, so I needed to observe for long enough to ensure that it wasn't just random and erratic, but in fact a pattern of behavior.
And I think that's perhaps what you might want to observe to draw any kind of conclusion.......an actual pattern, not just the daily fluctuations.