It depends on the demand Apple is expecting. For iPhones and iPads, demand is insane, therefore historically rollouts have been limited to "key countries" (US, Germany, UK, Singapore ...) about 1 week post the keynote, and about another week or two for second tier countries (Canada, Australia, Switzerland, ...)
As for Macbooks, you can expect a slightly faster rollout than that, and for any other products (Apple TV, accessories, software) you can expect same day.
But in the case of Macbooks at WWDC, you won't have to wait months. Apple usually pre-announces months ahead only if they need significant PR time, need to ramp up production, or are introducing a brand new category (say, a car...).