hello!
i don't know if you're still searching for a solution, but i think i found one
if you do /worldconfig daysPerMonth [1-99], you will get what you want !
i was having the same issue, and found this solution while searching thru the commands
also, just a tips, if you want to go for longer months, you might wanna use /worldconfig foodSpoilSpeed [0-10], default is 1 ! know that if you go for 0.5 you will have your food last as twice as you already have it
hope i helped!
ise