You will need a level 2 Bakery to make pies, and to get this "bronze" milestone/achievement, you have to make 50 pies over time, which looks to take 37:30 per unit max (if you don't have a good worker for this building). Overall, given that timing, it will take 31.25 hours at worst speed, but you will likely have a worker for this building by the time you get it to level 2.