I don't think that's it either. They don't often "trick" people like that. It says "after that, they decided.." as in after tea and snacks. I think that the pattern continues, that there IS a number of cubic inches in the 7th hour.
Okay, well maybe they straightened up the place lol. We don't know WHAT they continued to do for the next hour My thing is, they made it a point to say burrowing dirt in every sentence except the last one. That seems odd to me