I think it is an excellent idea...however what happens if someone forgets and makes a post.
That could be very embarrassing.
Is there any way that the threads can be temporarily locked?
Yes. We should make it a forced moment of.... internet silence. Because your personal reflection requires people to stop typing, even if it flies in the face of the first amendment.
Look if you want to take time during the day to reflect, by all means I understand it was a significant event for the country, and we should all do what we feel is best and right with our time. But please don't push what feels right for you on others. Some, like you, will want silence. Others will want more than anything to talk to someone at that time.
All I'm saying is that people with like-minded ideas on the topic should group together, and allow everyone else to do their thing as well.