MarcusNerva:

But after read both the Python and C++ source code, I didn’t find the iteration on ‘time’(i.e. the step on seq_len)


this loop exists, at the deepest level usually



 MarcusNerva:

And it seemed that all the time step of input features are calculated in parallel.


This is correct, non-recurrent input-to-hidden computations can be performed separately for better performance. Results of this are later used in hidden-to-hidden computation loop.