We present a process algebra suitable to the modelling of timed concurrent systems and to their efficient verification through model checking. The algebra is provided with two consistent semantics: a structural operational semantics (as usual for process algebras) and a denotational semantics in terms of Petri nets in which time is introduced through counters of explicit clock ticks. This way of modelling time has been called causal time so the process algebra is itself called the Causal Time Calculus (CTC). It was shown in a separate paper that the causal time approach allowed for efficient verification but suffered from a sensitivity to the constants to which counts of ticks are compared. We show in this paper how this weakness can be removed.