Thats wierd. What if you enter this code in a function node and connect an inject-node before it?
var d = new Date();
d.setDate(d.getDate() - 1);
d.setHours(d.getHours(), 0, 0, 0); // Date should now be 24h ago (on the hour)
node.warn(d.valueOf() / 1000);
return msg;
When you click on the inject node you should get a timestamp in the debug window with the current hour (on the hour) from yesterday.
Tip: If you are not fluid on timestamps, In the Node-RED debug window you can click on them to traverse through different formats.