How long before the game does the stadium open (for food)?

You can go early as 2 or 3 and just hang out

Check they're website to found out info.

Monday - Thursday: Chop House Gate and Premium Gates (servicing the SunTrust Club, Delta SKY360° Club and INFINITI Club) open two hours before the first pitch. All other gates will open 90 minutes before first pitch.  Friday: All gates will open two hours before the first pitch.  Saturdays: All gates will open three hours before the first pitch.  Sunday at 1:20 p.m.: Chop House Gate and Premium Gates (servicing the SunTrust Club, Delta SKY360° Club and INFINITI Club) open two hours before the first pitch.

I have been there at 5:30pm for a 7:20pm start time. Issue is not the STP, but some parking lots do not let you in before 5:30pm on a weekday. Hth.