stc:StartTime 

astronTime may be expressed in ISO8601 or as a double relative to a reference time

Element Information

Model

crd:Timescale , crd:RelativeTime{0,1} , crd:AbsoluteTime
Children: crd:AbsoluteTime, crd:RelativeTime, crd:Timescale

Source 

<xs:element name="StartTime" type="crd:astronTimeType" minOccurs="0">
  <xs:annotation>
    <xs:documentation>astronTime may be expressed in ISO8601 or as a double relative to a reference time</xs:documentation>
  </xs:annotation>
</xs:element>

Sample