CRM 2016 edit date/time field from TruClient with Javascript

// within LoadRunner TruClient
datum = new Date();
// access the iFrame from the top document
document.getElementById("contentIFrame0").contentWindow.Xrm.Page.getAttribute("scheduledend").setValue(new Date());
document.getElementById("contentIFrame0").contentWindow.Xrm.Page.getAttribute("scheduledstart").setValue(new Date());