Ehhhhh, I would disagree, though in practice it might be moot.

My sealant level check is generally every 6 weeks, but it's not because OS dries up, it's because it gets used via punctures. While I've had rear tires be bone dry at 8 weeks, I regularly have front tires, which are punctured far less frequently in my experience, lookin' fresh and full at 3 months. But, you've gotta schedule your checks around the shorter interval of the two tires and that's going to depend on your proneness to punctures (which is going to include ride frequency, mileage, road/debris conditions, etc).