Summary Some leading ideas of the constructivist protophysics are discussed on the basis of P. Janich's Protophysik der Zeit. After having reviewed the contents of the second edition Janich's claim that analytical philosophy of science is purely affirmative and not critical towards science in its historical appearence is refuted. In the next section the principles of constructivist methodology of physics are criticised, and the claim is refuted that prescriptions for measurement cannot without circularity be shown to be invalid by experimental (...) results. In the last section we discuss Janich's foundation of time measurement in a mathematical frame similar to that for extensive systems. Thus the relation between Janich's and the ordinary account is cleared up. (shrink)