I am using page 28 of this doc for reference: https://resources.docs.salesforce.com/200/latest/en-us/sfdc/pdf/bi_dev_guide_saql.pdf

I need to change the time zone in the step. I am trying to use the computeExpression action to handle it. Here is the code I tried: 

     "CreatedDate_Hour_3": {
                "datasets": [
                    {
                        "id": "0Fb32000000TVRzCAO",
                        "label": "Case_Article_Survey",
                        "name": "Case_Article_Survey",
                        "url": "/services/data/v38.0/wave/datasets/0Fb32000000TVRzCAO"
                    }
                ],
                "isFacet": true,
                "isGlobal": false,
                "query": {
                    "pigql": "q = load \"Case_Article_Survey\";\r\nq = group q by 'CreatedDate_Hour';\r\nq = foreach q generate 'CreatedDate_Hour' as 'CreatedDate_Hour', count() as 'count';\r\nq = order q by 'CreatedDate_Hour' asc;\r\nq = limit q 2000;",
                    "measures": [
                        [
                            "count",
                            "*",
                            "count"
                        ]
                    ],
                    "action": "computeExpression",
                    "parameters": {
                        "source": "CreatedDate_Hour",
                        "mergeWithSource": true,
                        "computedFields": [
                            {
                                "name": "CreatedDate_Hour_adjusted",
                                "type": "Datetime",
                                "format": "MM/dd/yyyy HH:mm:ss",
                                "saqlExpression": "toDate(CreatedDate_Hour  - 8*3600)"
                            }
                        ]
                    },
                    "measuresMap": {},
                    "autoFilter": true,
                    "groups": [
                        "CreatedDate_Hour"
                    ]
                },
                "selectMode": "single",
                "type": "aggregateflex",
                "useGlobal": false,
                "visualizationParameters": {
                    "options": {}
                }
            },


This code is not subtracting 8 hours from CreatedDate_Hour.