Yes I arrive around 8AM and leave around 8PM so I assume I have 7-8ish hours of eating possibly slightly less. Given about 1-1:15 for train ride in and out.
Haneda or Narita? Gonna assume Narita based on your train rides.
Agree that train station eating will be the most efficient way to get some great grub in, as many places will need reservations ahead of time. Ramen, izakaya and shokudo dining usually don’t require rezzies, and ramen cultures in Japan generally involves especially fast seat turnovers.
Though it is a bit west of central Tokyo, consider Shinjuku also, since there are lots of depatos (Takashimaya, Isetan, etc.), each with their own depachikas to peruse.