In the upcoming release we will be including GetDetails and GetAllDetails to retrieve more information on the sub layers.For the time-being, you can create a FeatureLayer with URL: ArcGISDynamicMapService.Url + Layer.ID. You will have this metadata when the layer is initialized.
FeatureLayer l = new FeatureLayer()
{
Url = string.Format("{0}/{1}", ArcGISDynamicMapService.Url, Layer.ID)
};
l.Initialized += (s, e) =>
{
var layerInfo = l.LayerInfo;
var timeExtent = l.TimeExtent;
};
l.Initialize();