Timestamp in my trace event .json file does not match after loading in the chrome://tracing/

Question

From the excerpt of my trace_file.json

[
  {
    "args": {
      "core": 0,
      "opKind": "aicconvolutiond32",
      "opMemory": "TCM",
      "opName": "Conv_323__2_fc__2_tile_0__1",
      "opOperand": [
        "Conv_323__2_fc__2_tile_0__1_res@ui8",
        ...
        " Conv_323__2_fc__2_tile_0__1_vtcmin8_res@i8"
      ],
      "opResource": "HMX",
      "opShape": [
        "Dest [1 x 1 x 1 x 5 x 2048]",
        ...
        " Unnamed10 [1 x 5 x 4096]"
      ]
    },
    "cat": "Conv_323__2_fc__2_tile_0__1",
    "dur": 1.041667,
    "name": "Conv_323",
    "ph": "X",
    "pid": 103,
    "tid": 2,
    "ts": 617480883719.4166
  },
  {
    "args": {
      "core": 0,
      "opKind": "aicconvolutiond32",
      "opMemory": "TCM",
      "opName": "Conv_323__2_fc__2_tile_0__1",
      "opOperand": [
        "Conv_323__2_fc__2_tile_0__1_res@ui8",
        ...
        " Conv_323__2_fc__2_tile_0__1_vtcmin8_res@i8"
      ],
      "opResource": "HMX",
      "opShape": [
        "Dest [1 x 1 x 1 x 5 x 2048]",
        ...
        " Unnamed10 [1 x 5 x 4096]"
      ]
    },
    "cat": "Conv_323__2_fc__2_tile_0__1",
    "dur": 1.041667,
    "name": "Conv_323",
    "ph": "X",
    "pid": 104,
    "tid": 2,
    "ts": 617480883719.4166
  },
  {
    "args": {
      "core": 0,
      "opKind": "aicconvolutiond32",
      "opMemory": "TCM",
      "opName": "Conv_323__2_fc__2_tile_1__1",
      "opOperand": [
        "Conv_323__2_fc__2_tile_1__1_res@ui8",
        ...
        " Conv_323__2_fc__2_tile_1__1_vtcmin8_res@i8"
      ],
      "opResource": "HMX",
      "opShape": [
        "Dest [1 x 1 x 1 x 5 x 2048]",
        ...
        " Unnamed10 [1 x 5 x 4096]"
      ]
    },
    "cat": "Conv_323__2_fc__2_tile_1__1",
    "dur": 0.260417,
    "name": "Conv_323",
    "ph": "X",
    "pid": 103,
    "tid": 2,
    "ts": 617480883720.7188
  },
  {
    "args": {
      "core": 0,
      "opKind": "aicconvolutiond32",
      "opMemory": "TCM",
      "opName": "Conv_323__2_fc__2_tile_1__1",
      "opOperand": [
        "Conv_323__2_fc__2_tile_1__1_res@ui8",
        ...
        " Conv_323__2_fc__2_tile_1__1_vtcmin8_res@i8"
      ],
      "opResource": "HMX",
      "opShape": [
        "Dest [1 x 1 x 1 x 5 x 2048]",
        ...
        " Unnamed10 [1 x 5 x 4096]"
      ]
    },
    "cat": "Conv_323__2_fc__2_tile_1__1",
    "dur": 0.260417,
    "name": "Conv_323",
    "ph": "X",
    "pid": 104,
    "tid": 2,
    "ts": 617480883720.7188
  }
]

Now when I load the same trace file in chrome://tracing/ I see the start time does not coincide with the value of ts in the trace file. "ts": 617480883719.4166 in .json file and Start in snapshot is 2,908,417 ns.

???

Can some one help me how chrome tracing is normalizing\factorizing that "ts" value?