It’s been said many times in the TR forum, FTP isn’t what a person can hold for 1 hour exactly. It can vary per rider, and can be anything from 40 to 70 mins or more.
However, some folk in their wisdom thought it would be “fun” to compare the ramp test ftp estimate with an actual hour of power (silly people!):
I got sick two days after my effort and had to take a week off! Not sure if was a coincidence or as a result of going that hard for an hour.