Gstreamer and OpenCV loading times

I’m working on an application that connects to an RTSP stream using Gstreamer and sends the frames to OpenCV. In this case OpenCV handles the display of the frames on screen, my question is the following:

Since part of this process has been parallelised in other parts of my code through threading, thus streams start to connect and execute in parallel.

When the multiple windows of each stream appear in the screen, which should be the correct behaviour ?
Will they appear all at the same instant, or will they start one after the another ?

Thank you