Good catch and a good example of writing with an idea in your head and not getting it onto the page. The sub is surfaced, so that it can be seen on satellite by Russia for the launch as the point is a public demonstration, not a covert launch. But I shoulda said that as above.
Surfacing 3 hour early is just asking for an air borne ASW asset to kill it. I can see it popping up say maybe 10-15 early for the plot point there. Another thing to consider sub launched munitions usually don't work unless fired from underwater. They are not normally designed to be launched from the open air.
