There are currently two options for ArcGIS online users to display time enabled data: cumulatively and by interval; it is not possible to display only the data for a single point in time. In ArcGIS API for JavaScript 3.27, however, there is an option to create a time slider with a single thumb that displays an instant in time (singleThumbAsTimeInstant). Please add this as an option in ArcGIS online and the Time Aware application so those of us who are not developers can display data for a single moment in time.
