I think this is a shortcoming of the national map API rather than sliderule, but wanted to document that it's not obvious timestamps returned from raster.sample are when the product was 'last updated' rather than when the data was acquired.

region = [  {"lon": -108.34, "lat": 38.89},
            {"lon": -107.76, "lat": 38.90},
            {"lon": -107.78, "lat": 39.26},
            {"lon": -108.36, "lat": 39.25},
            {"lon": -108.34, "lat": 38.89}  ]

geojson = earthdata.tnm(short_name='Digital Elevation Model (DEM) 1 meter', polygon=region)
gdf = raster.sample("usgs3dep-1meter-dem", [[-108.1,39.1]], {"catalog": geojson})
gdf

This is inconsistent with other APIs where 'time' is observation time of the data.

The timestamps are coming from here

Unfortunately I don't think the national map api keeps track of the nominal acquisition date of a given 1m tile?...