Runtime entering dates by user

I want to enter start and end date but I don’t want to create separate entity for that which stores in database. But I am unable to do that Cause it shows error How to solve following error. That is without storing dates in attribute I want it should be taken at random.     or how to configure following fields.
1 answers

To display fields, you must use an entity, that’s a requirement.

If you don’t want to store the data in database, you should use a separate entity for these dates, and make this entity Not persistable.