1) There is no yield point for hyperelastic material model
2) I think most people would say that a linear viscoelastic material does not have a yield point either. Yielding is the onset of permanent deformation and requires some form of plastic deformation.
3) Failure is not given by a strain energy density.
4) The time scale does not matter for hyperelastic materials
5) The time scale needs to be correct for viscoelastic materials. The "correct" time is typically the real physical time.
Jorgen Bergstrom, Ph.D.