[Nurdok]

You can ask the person you wish to prove current time to, to provide a "challenge" that you will film ("put two fingers up", "hold up a USB cable").

[dosshell]

I don't understand how this proves anything? What is stopping me from holding up the USB cable two years later?

[Apreche]

You are live streaming. Someone asks you to do something, but you don't know what they are going to ask. You do the thing that they have requested live on stream, e.g.: Holding up a USB cable. That person who made the request knows that you did not know what they were going to request, so they know that they are watching a live stream and not a recording.

However, third parties watching the stream have no proof that this wasn't a coordinated trick prepared in advance.