A begs too...we often do 2 separate lessons per day, and repeat sessions as well. I just don't do them back to back! If she really wants more I pretend to be shocked. (What!? You want MORE math?! You LOVE your math!) then I pretend to think about it and 'let' her win...but I say okay, but first Mommy needs a drink..or a bathroom break...anything to give a few minutes between.
I decided that since A started later, her attention span/ interest is greater tha if she were doing it as an infant (mostly

) that as long as she wanted it and was enjoying it, why would I discourage that?
We don't do more than two days worth of material in one day though because I really want to make sure she gets it. Since she wants more, I often start by repeating the previous days 2nd session 1 time. This way she gets more, not repeated so many times as to bore her, but ensuring we aren't missing too much by speeding up...
I think your best predicter of how fast is the enjoyment/ interest level of your LO...but I have also always stopped when she still wants more to build anticipation...when A was learning body parts we had a Mr. Potato Head toy. She was too young to play with it on her own (she was six mo), so I only brought it out with mommy. I quickly learned that these 'special' activities were highly prized and much anticipated. I have tried to remember this lesson in teaching...
So glad she is excited...Also, you can make the math spots be moons!