I have a Google smart home app released that supports various light bulb brands. I have a user with 5 Phillip Hue light bulbs and there are approximately 1360 query state requests per day for the 5 bulbs. Is this frequency of query requests common and expected for all devices?
That's one query request every ~5 minutes.
https://developers.google.com/actions/smarthome/develop/process-intents#QUERY
It is normal for Google to periodically send QUERY intents to your service to ensure that the data in Home Graph is up to date. You can mitigate this process by making sure that you have implemented Report State to publish all relevant state changes to Google in real time, as this also directly updates the state in Home Graph.
The actual frequency is a bit more difficult to pin down as it relates to not only how often you report state for devices, but also user activity on those devices. Generally speaking, the more often you report state to Google the less you should see QUERY polling.
We are also actively working on ways to reduce the need for QUERY polling, so in the future you should see the frequency of this reduced so long as you have Report State implemented for all your users' devices.