My reaction looking at this plant, in what I would consider a very small pot, and the pot being unglazed, I go the other way. I think it needs water more often. I always keep Sans from drying out but have had times when I didn't water that often and saw similar effects.
I'm watering my Sans @ work twice per week because the air is so dry in here, and they are in plastic because I don't want to risk them breaking a clay pot. Regardless of the interval, which there is no way for us to determine, there is no benefit to your plant in waiting longer after the soil has lost most of its moisture to add more water.
