Hi, we do not have strict limits right now.  Feel free to call the API route as often as once every 5-6 seconds (you will just identical responses in a smaller time frame) or less often based on your game's needs. Don't worry about optimizing your API calls.
 
By the way, it's great that your are learning to use APIs. It's an excellent skill to have. If you need help or have any technical questions I am here to help. Feel free to let me know what programming language and/or engine you are using and I may be able to give you some tips.