Amp html 如何获得放大器中的时差

我必须在amp analytics中发送两个日期之间的时差（extraUrlParams中的t）

<amp-analytics type="googleanalytics">
        <script type="application/json">
        {
        "requests": {
            "event": "abc.com"
        },
        "extraUrlParams": {
            "t":"(time difference)",
            "cat": "Amp_UsedCarSearch",
            "act":"Clicked",
            "lbl":"test"
        },
        "vars": {
            "account": "abc"
        },
        "triggers": {
            "trackMakeOfferClicks": {
            "on": "click",
            "selector": "#abc",
            "request": "event"
            }
        }
        }
        </script>
    </amp-analytics>