Estoy usando el gráfico de Grantt de (highcharts.com) de forma predeterminada, la clave de fecha de inicio y finalización del objeto que acepta valores usando la función javascript date().gettime. Quiero pasar formatos de fecha como '2021-09-20' para poder crear un objeto json desde el backend de php. He creado una llamada ajax para que se obtenga de un backend y aparezcan los datos de respuesta en serie.

// EL GRÁFICO

 <script type="text/javascript"> Highcharts.ganttChart('container', { chart: { styledMode: true }, title: { text: 'Highcharts Gantt in Styled Mode' }, subtitle: { text: 'Purely CSS-driven design' }, xAxis: { min: today.getTime() - (2 * day), max: today.getTime() + (32 * day) }, series: [{ name: 'Project 1', data: [{ name: 'Planning', id: 'planning', start: '2021-09-20', end: '' }, { name: 'Requirements', id: 'requirements', parent: 'planning', start: today.getTime(), end: today.getTime() + (5 * day) }, { name: 'Design', id: 'design', dependency: 'requirements', parent: 'planning', start: today.getTime() + (3 * day), end: today.getTime() + (20 * day) }, { name: 'Layout', id: 'layout', parent: 'design', start: today.getTime() + (3 * day), end: today.getTime() + (10 * day) }, { name: 'Graphics', parent: 'design', dependency: 'layout', start: today.getTime() + (10 * day), end: today.getTime() + (20 * day) }, { name: 'Develop', id: 'develop', start: today.getTime() + (5 * day), end: today.getTime() + (30 * day) }, { name: 'Create unit tests', id: 'unit_tests', dependency: 'requirements', parent: 'develop', start: today.getTime() + (5 * day), end: today.getTime() + (8 * day) }, { name: 'Implement', id: 'implement', dependency: 'unit_tests', parent: 'develop', start: today.getTime() + (8 * day), end: today.getTime() + (30 * day) }] }] }); </script>