Modify "process_to" during execution

Modify "process_to" during execution

Hello, 
I am currently working on the Python version of metavision_vibration_estimation.

When launching the executable, we can specify the argument "process_to" to define the acquisition time.  Is it possible to modify the value of this variable during the execution of the code ? 

I would like to open the camera stream. Then define ROIs and finally press a key on the keyboard to launch the acquisition duration specified with "process_to".

So I would like that the value "process_to" stays at None until the user interventions. 
Is there a way to modify the value during the execution while keeping the same iterator (mv_iterator) ?

Thanks for your help