Tilemap Torque

[normanb]

I am working on adding a custom backend using the tilemap specification, I am looking at the tilejson example in this repo. Start and End are set as negative

{
"start": -1796072400000,
"end": -1414843200000,
"resolution": 2,
"data_steps": 861786,
"column_type": "date",
"tiles": ["http://{s}.ashbu.cartocdn.com/viz2/api/v1/map/cf28c540d3cf15a29a759f84ff440679:0/0/{z}/{x}/{y}.json.torque"]
}

and an example object

{"x__uint8":60,"y__uint8":38,"vals__uint8":[1],"dates__uint16":[471]}

the suffix _uint8 and _unit16 isn't documented and how does 471 in the dates field correspond to a date between start and end?