Is there always a sequential nature of time-stepping?
OP essentially asks if sequential time stepping for numerically solving a PDE is a necessity or not. OP describes this general issue from a concrete perspective which probably seems like lacking in details. Nevertheless, the question is general at its core and already has a nice answer that presents approaches alternative to sequential time-stepping.
There is no comment that would explain what would the optimal shape of the question with more "details or clarity" be. In my mind, the question is clear enough to anyone capable of answering it. The optimal outcome would IMHO be to open the question and accept the current answer.