I am able to watch on nbcolympics.com and if you drag the “play bar” to the left you can start at any point. I would assume this will only work while the live is still live at some point.
It would be nice if there are archives of streaming, but honestly I wouldn’t expect it until after the games are over simply because the more that is archived the more that are on the site downloading and it will slow down the live streaming for everyone. Even with cloud servers there is only some much bandwidth.