You're correct. It looks like it's expecting the time to be in Epoch time format. I was able to get it formatted using a content function
const currentClosuresTemplate = {
title: "Current Road Closure Info",
content: formatContent,
outFields: ["*"]
};
function formatContent(feature) {
let street_name = feature.graphic.attributes.STREET_NAME;
let date_to = new Date(feature.graphic.attributes.DATE_TO);
return street_name + "<br> Closed until " + date_to.toLocaleString();
}
Note that you have to specify outFields in 4.12 when using a function.