With the observations endpoint this is entirely dependent on how often a station reports data. Some stations will report every hour while others can report every minute. Our system will have the latest observation ready for you as soon as it becomes available. In the observations/summary endpoint, which is derived from observations, we update this data every 15 minutes based on all observations received in the previous 15 minutes.
Forecast data is updated every hour in the US and every 6 hours outside of the US.
These are the most common endpoints brought up when clients ask about update intervals. If you have another endpoint in mind you'd like to discuss, please feel free to reach out to our support staff.