It's under the Edit tab, then Preferences>AutoSave. I put mine on 7 minutes, with 75 autosaves, but if I were doing the huge hex file that you have, would autosave every 3 - 4 minutes. You can change it back when your file size isn't so big.
However, since my laptop is about 9 yrs old, win 7 and on death's door, I automatically hit the save button every 2 - 3 minutes, have learned my lessons. I also keep a copy of the entire file myself, and every 15 minutes or so I do a save as. (I tend to do stupid stuff and delete the wrong object, yada yada, then decide I liked the older one better).