I generally believe product strategies should be evaluated more frequently the earlier a product is in its lifecycle. A zero-to-one team I worked closely with found the right pace to be testing a new direction & goals every month or so, whereas a scaled team I led had sufficient visibility to establish a high-level strategy that lasted well past a year.
At Patreon, we aim to set strategies & goals that cover 6 months or so for each team. In tech, unless you're working on a platform or infra initiative that is largely independent of evolution in user need, I'd generally recommend somewhere between 3-6 months for early-stage or growth companies and 6 months to a year for more mature companies.
At each of those milestones, I'd suggest confirming your core assumptions about your customer, the problem space, the competitive landscape & your strategy to maintain or grow your market position. If any of those elements change in a fundamental way during that window, you should consider whether you need to update your product strategy even if it's not quite on schedule.
