When you open a feast and all the slots are used (10 for nc / 15 for guild) the feast automatically end ...
It's totally useless wait for 5 mins when in the first 15 secs the feast have 0 slots
So, until the feast have at least 1 slot, the 5 minutes rule will keep active, but in the same moment that someone eat the 10th slot, the feast end automatically to keep users wasting time ^^