Magento 2.4.x add system.config date field using ui component

In Magento 2.4.x, How to add date time field in Content -> Design -> Config-> HtmlHead. I tried below code it is showing in UI. but its not saving.

    <field name="message_valid_from">
        <argument name="data" xsi:type="array">
            <item name="config" xsi:type="array">
                <item name="dataType" xsi:type="string">string</item>
                <item name="label" xsi:type="string" translate="true">Demo Message Valid From</item>
                <item name="formElement" xsi:type="string">date</item>
                <item name="source" xsi:type="string">page</item>
                <item name="sortOrder" xsi:type="number">21</item>
                <item name="dataScope" xsi:type="string">message_valid_from</item>
                <item name="validation" xsi:type="array">
                    <item name="required-entry" xsi:type="boolean">false</item>
                </item>
                <item name="options" xsi:type="array">
                    <item name="dateFormat" xsi:type="string">yyyy-MM-dd</item>
                    <item name="timeFormat" xsi:type="string">HH:mm:ss</item>
                    <item name="showsTime" xsi:type="boolean">true</item>
                </item>
                <item name="storeTimeZone" xsi:type="string">string</item>
            </item>
        </argument>
    </field>