An hour? That’s way too much time.
Give ‘em 15 minutes AT MOST, just so the media heads freak out with no time to spin.
The sense of total panic needs a bit of time to build.
I’m thinking the other way around. 3-4 hours beforehand would give time for panic to set in as the new dump circulates on social media and pro-Sanders sites. Only 15 minutes they could brush it off as if they hadn’t heard yet.