espocrm-base/application/Espo/Resources/metadata/fields/duration.json

{
    "params": [
        {
            "name": "default",
            "type": "int"
        },
        {
            "name": "options",
            "type": "arrayInt"
        }
    ],
    "notCreatable": true,
    "fieldDefs": {
        "type": "int"
    }
}