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

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