Without the premium upgrade, the weather data refreshes itself once every 4 hours - but the complication display continues to update every hour on the hour with the forecasted weather for that hour, so it won't really be that out of date. (The subscription is unfortunately necessary from a business standpoint - each data refresh costs a small amount of money, and this quickly adds up since the complication is updating itself every 30m of every day. It was either add a subscription or not have a complication at all!)