If temporary formulas are a part of your use case, utilize the Time To Live setting for your instances.  To use this setting, provide the amount of time a formula instance should exist in seconds. After this amount of time has lapsed, the formula instance is automatically deleted.  

To configure a formula instance for automatic cleanup, you should include the following in your payload:

"settings":{"formula.instance.time.to.live": <Number of seconds to keep instance>}

Formula instances created without this will effectively have an infinite time to live (they will never be automatically deleted).

The time to live setting can only be changed via the API.  The UI does not currently support this capability.