QGIS 3.14
Old version:
for i, layer in enumerate(QgsProject.instance().mapLayers().values()):
if isinstance(layer, QgsRasterLayer):
mode = QgsRasterLayerTemporalProperties.ModeFixedTemporalRange
tprops = layer.temporalProperties()
tprops.setFixedTemporalRange(QgsDateTimeRange(QDateTime(QDate(2020, 1, 1), QTime(1, i, 0, 0), Qt.UTC),
QDateTime(QDate(2020, 1, 1), QTime(1, 1+i, 0, 0), Qt.UTC)))
tprops.setMode(mode)
tprops.setIsActive(True)
https://github.com/Mariosmsk/qgis-python