question

Technically, nothing can be "unlimited" regardless of what type of agreement you have with us, since there will always be a limit somewhere. In the case of Cloud Script, there are a few different ways it can be called - from the client directly, via a PlayStream action, or from Photon Realtime as a webhook. Assuming you mean directly from the client, the default free tier limit on total CPU time for any given Cloud Script call is shown on your Settings->Limits tab (currently 5 seconds). In terms of how frequently you can call a Cloud Script from the client, as long as you're waiting for the response from the previous call, you could make a few calls in sequence. But over the lifetime of the player session, the calls should average out to something like a couple per minute (per player).

Cloud Script is designed for small, lightweight logic. If what you need is more of a realtime updating system where the player is frequently updating some data, you should have a look at using a custom game server, so that you can pull all the data needed for the player session, updating the client as often as needed while updating the backend data only periodically (when key points are reached in the gameplay experience, or after a couple of minutes otherwise).