The Two Towers

Completion
For the first part, the second mushroom will usually be discovered when using the 3rd machete after finding the first mushroom.

For the second part, each mushroom takes 3 hours to chop down, but can be done simultaneously using two helpers.

For the third part, each tower takes 4 hours to construct. These cannot be done simultaneously, and so it will take a total of 8 hours to complete this part of the quest.