I didn't understand what you really want.
First you say that you need a temporal property(I believe that would be an attribute that is not persisted, this can be achieved using @Transient annotation)
Then you say that, when you restart your app sv it creates a new field, so, if you restart your application twice, it needs to create it twice? I relly missed something here...
Then the property should not be included in the table(need to create the field but can't persist it, is it?)
I really did not understand, BUT with you want to create a non persistent field in an entity class, just mark it with @Transient annotation.
Hope it helps,