The flow looks like this:

The contents of the Nodes are as follows:

Here's the flow:

$ ppjson < .node-red/lib/flows/HTTP-GET-Example
[
  {
    "id": "e116677c.1ee998",
    "type": "inject",
    "z": "c85b2010.37a4e",
    "name": "",
    "topic": "",
    "payload": "",
    "payloadType": "date",
    "repeat": "",
    "crontab": "",
    "once": true,
    "x": 120,
    "y": 80,
    "wires": [
      [
        "9367f7e8.6c9808"
      ]
    ]
  },
  {
    "id": "998e7b3.f667188",
    "type": "debug",
    "z": "c85b2010.37a4e",
    "name": "",
    "active": true,
    "console": "false",
    "complete": "payload",
    "x": 690,
    "y": 160,
    "wires": []
  },
  {
    "id": "9367f7e8.6c9808",
    "type": "function",
    "z": "c85b2010.37a4e",
    "name": "Date to String",
    "func": "var d = new Date(msg.payload);\nmsg.date = d.toISOString();\nreturn msg;",
    "outputs": 1,
    "noerr": 0,
    "x": 280,
    "y": 80,
    "wires": [
      [
        "4919d9e7.b6e628"
      ]
    ]
  },
  {
    "id": "efc196dc.103e68",
    "type": "http in",
    "z": "c85b2010.37a4e",
    "name": "",
    "url": "/hello",
    "method": "get",
    "swaggerDoc": "",
    "x": 100,
    "y": 160,
    "wires": [
      [
        "fcc0e674.033f18"
      ]
    ]
  },
  {
    "id": "fcc0e674.033f18",
    "type": "http response",
    "z": "c85b2010.37a4e",
    "name": "",
    "x": 250,
    "y": 160,
    "wires": []
  },
  {
    "id": "4919d9e7.b6e628",
    "type": "http request",
    "z": "c85b2010.37a4e",
    "name": "",
    "method": "GET",
    "ret": "txt",
    "url": "http://localhost:1880/hello?ts={{date}}",
    "tls": "",
    "x": 510,
    "y": 80,
    "wires": [
      [
        "46464921.b9b9b8"
      ]
    ]
  },
  {
    "id": "33b01e6d.cc4fe2",
    "type": "comment",
    "z": "c85b2010.37a4e",
    "name": "1. Format a Time Stamp String, trigger HTTP GET",
    "info": "",
    "x": 230,
    "y": 40,
    "wires": []
  },
  {
    "id": "46464921.b9b9b8",
    "type": "function",
    "z": "c85b2010.37a4e",
    "name": "Add Status Code",
    "func": "msg.payload = JSON.parse(msg.payload);\nmsg.payload.statusCode = msg.statusCode;\nreturn msg;",
    "outputs": 1,
    "noerr": 0,
    "x": 690,
    "y": 80,
    "wires": [
      [
        "998e7b3.f667188"
      ]
    ]
  },
  {
    "id": "b740a4d8.48bf58",
    "type": "comment",
    "z": "c85b2010.37a4e",
    "name": "3. Respond to the HTTP Request",
    "info": "",
    "x": 170,
    "y": 120,
    "wires": []
  },
  {
    "id": "ca38baaa.35c748",
    "type": "comment",
    "z": "c85b2010.37a4e",
    "name": "2. Pick up the Response, Add Status Code",
    "info": "",
    "x": 600,
    "y": 40,
    "wires": []
  },
  {
    "id": "aa43884c.55bc78",
    "type": "comment",
    "z": "c85b2010.37a4e",
    "name": "4. Display the Date and Status Code",
    "info": "",
    "x": 580,
    "y": 120,
    "wires": []
  }
]