How do I get the start time

how do I get the start time and end time of a workflow exercise and send it to slack?

Example message:

start: 37 minutes and 9 seconds
end: 37 minutes and 14 seconds

Check the example below:

{
  "nodes": [
    {
      "parameters": {},
      "name": "Start",
      "type": "n8n-nodes-base.start",
      "typeVersion": 1,
      "position": [
        250,
        300
      ]
    },
    {
      "parameters": {
        "functionCode": "return [{ json: { start: new Date().toISOString() } }]\n"
      },
      "name": "Function",
      "type": "n8n-nodes-base.function",
      "typeVersion": 1,
      "position": [
        480,
        300
      ],
      "notesInFlow": true,
      "notes": "Get Start"
    },
    {
      "parameters": {},
      "name": "NoOp",
      "type": "n8n-nodes-base.noOp",
      "typeVersion": 1,
      "position": [
        750,
        300
      ],
      "notesInFlow": true,
      "notes": "Do Your Thing"
    },
    {
      "parameters": {
        "functionCode": "return [{ json: { end: new Date().toISOString() } }]\n"
      },
      "name": "Function1",
      "type": "n8n-nodes-base.function",
      "typeVersion": 1,
      "position": [
        1000,
        300
      ],
      "notesInFlow": true,
      "notes": "Get End"
    },
    {
      "parameters": {
        "attachments": [],
        "otherOptions": {}
      },
      "name": "Slack",
      "type": "n8n-nodes-base.slack",
      "typeVersion": 1,
      "position": [
        1240,
        300
      ]
    }
  ],
  "connections": {
    "Start": {
      "main": [
        [
          {
            "node": "Function",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Function": {
      "main": [
        [
          {
            "node": "NoOp",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "NoOp": {
      "main": [
        [
          {
            "node": "Function1",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Function1": {
      "main": [
        [
          {
            "node": "Slack",
            "type": "main",
            "index": 0
          }
        ]
      ]
    }
  }
}