When you configure a layer's pop-up in ArcGIS Online's map viewer there's a checkbox to add/remove the time from a date field. If you go with the default and don't include time should you choose to build an application with the Web AppBuilder for ArcGIS there will be a conflict if you try to include a query on this date field. In the Web AppBuilder the default, and only, format for a date field is date & time. There isn't an option to exclude time. Therefore when I try to query the date field for a specific date no results will show.