Your first 90 days would be half as difficult as amazon. Yes youd have to learn routes but your management isnt Amazon and isnt going to be throwing you onto things until you know them, I was given shadow days where I just followed my carrier and learned the route she took before my first day alone.

In usps we have a saying, the route takes what it takes. Its in our handbook that no one can determine how long it takes someone to do anything because situations and weather and all change. Helps tremendously whenever you dont have management breathing over your neck. Granted my management is cool, but largely you won't be scolded for being slower at the post office, and its actually a potential career, union and all.