I mean, the 6 month patch cycle thing only really applies if the expansion is going to have 4 raid tiers (24 month long expansion = 4 x 6 month raid tiers). 4 raid tiers per expansion isn't a standard/normal thing - BfA and WoTLK were the only expansions that had that, and I really think part of why they did the 4 raid tiers in BfA was with how poorly the expansion was perceived/launched, they felt they needed them to make it last 2 years. If they are going back to a more normal 3 tier expansion, 8 months or so (and a patch in July-ish) would be normal.