This is the timeout for FIMC to wait for the new frame to produce. 1000/25 is a timedifference between frames at 25 fps. If no frame would be returned the function will proceed further not having a frame to show. Something like nonblocking output for FIMC.
This was here at the time while video output was hellofa slow for unknown reason (turns out to be unrelevant to FIMC and a problem of testing device type). I would advise @mihailescu2m to change it to the same "1000" MFC has and feed it some 1080p video that works fine at "1000/25". If this is still needed the video would stall deadlocking the buffers (dequeued more than queued back and no buffers to fill).