So far aside from the 1-2 Splatfests, all Splatfests have been 3 weeks apart. So the next Splatfest actually will fall on Halloween this month. If you want to see a list of all the Splatfest dates for the rest of this year and next year I made a list for people to check. However if there's ever a delay for Splatfest the dates will be changed.