If I recall correctly and the code hasn't been changed...
The number is for five days (from when harvests were every five days, and it's not an easy thing to go in and change all the numbers), not seven. It is then further modified by the season and weather. I don't know the whether modifiers, but Kelley has been running the spreadsheets for several harvests in Arcaea and came up with 25% for Winter, 75% for Spring, 100% for Summer, and 200% for Autumn.
So, the formula, so far as I know...Region food number * 7/5 * season percentage * weather modifier * production percentage at each full turn = harvest number
