I have not read any cases where a miscellaneous face in a crowd visible for 3 frames was able to sue anyone in a legal case. Perhaps you could provide an online link to such a history.
I think this is leading into a gray area as I wouldn't want to see myself for 3 frames in an ad supporting a republican party (or democratic *cough*).
What is the actual time "allowed" for an identifiable face to be displayed without having grounds for a lawsuit? I doubt that a company is "permitted" to take photos of people on public grounds and compile a time lapse without their consent just because the faces are shown for only 3 frames.
I thought, as long as the person can recognize him-/herself you need a release - period. If no release is available it will be editorial (if possible). Especially in time lapse videos it's easily possible to process the footage in a way to make the people unrecognizable - I thought that would be the requirement for RF. But obviously it's just enough to "be part of a crowd". Now let's define crowd (*getting a headache*).
I highly doubt that this is written anywhere which may be a good and a bad thing at the same time for us photographers. However, in order to be able to publish legally safe content it would be of great help if there would be official statements made by the agencies accepting such content (most likely footage).
Or shall we just upload anything hoping that the agencies will make the decisions for us?