This question has been answered by mleipoldhaas. See the first response.
[{
"caption":"Operating Hours",
"fields": [
{"field":"day", "caption":"Day"},
{"field":"from", "caption":"From"},
{"field":"until","caption":"Until"}
]
}][
{"header": "Day", "width": "60", "sortable": "false", "dataIndex": "day"},
{"header": "From", "width": "50", "sortable": "false", "dataIndex": "from"},
{"header": "Until", "width": "50", "sortable": "false", "dataIndex": "until"}
]