I get stints where I am hungry a lot and so I eat a lot more. And I have stints when I'm not that hungry and so I eat less. I listen to my body and it seems to work. Another thing I have noticed is there are two kinds of hunger pangs. One is a slight bit of pang coming around the time I usually eat, as if my stomach is reminding me it's the usual time. Often, if I ignore that, it passes and then I can go hours before I get hungry again. That kind of hunger pang is more like a pang that comes out of habit. The other kind of hunger pang is the kind that if I ignore it, it keeps coming back and back and nagging me to no end and all I can think about is food food food for hours. All I can think about is food all the time for long hours. It's very annoying and I take that is evidence that my body is very very interested in food that day. So I listen and I eat.
If you are exercising a lot, it's natural to be more hungry. My instinct is to say eat more if you are REALLY hungry and see how that goes. I personally do not worry about what time it is when I eat. If I am really hungry and it's midnight, then I eat. If it's dinner time, but I am not hungry, then I don't eat. If you follow your hunger and eat healthy and do not start getting flabby, then it's most likely the right track for you.
Also, nutrition density is going to be very important for muscle building. I think fitday.com is very useful to monitor nutrient intake and where you may be lacking, but not useful for monitoring caloric needs. According to fitday, I should be getting fatter, not skinnier. But yet I am getting skinnier so that shows you what fitday knows about my caloric needs (ie nothing). Fitday can't tell you how many calories you need because metabolism and exercise and caloric expenditure vary hugely across individuals. Your hunger and a look in the mirror will go much farther towards telling you what you need than any fitday math formula ever will.
Edited to add: Many paleo eaters advocate fewer meals per day, which is fine by me under most circumstances. However, if doing such results in a person not being able to stuff down sufficient calories and therefore becoming underweight and often hungry, then by all means, eat more meals and get the calories you need if that is what you need to do!