Not entirely correct. The box office opens at 10 am every morning to buy general admission tickets or upgrade to reserved. However, the best way to get GA tickets is to buy them from someone off of the street and save the time waiting in line to buy. All GA tickets are the same and can be used for any session.
The GA gate opens 2 hours before the game and the first 5500 are allowed to enter. We showed up 1.5 hours before the game started both times and had no problem getting a seat in the OF.
From the website:
"GA tickets are not designated for a specific game or date and seating is available on a first-come, first-served basis. As long as the ticket holder arrives early enough to be seated, the tickets are good for all games, including finals games. If the GA seating sections are filled to capacity, the gates will close. Stadium staff will then implement a one-out, one-in policy."