I'm blind.
For future reference, you can in 8.1.
http://msdn.microsoft.com/en-us/library/windows/apps/windows.devices.geolocation.geocoordinate.aspx
see PositionSource
PositionSourceTimestamp
Read-only Gets the time at which the associated Geocoordinate position was calculated.
http://blogs.msdn.com/b/thunbrynt/archive/2014/04/22/windows-phone-8-1-for-developers-geolocation-and-geofencing.aspx
From the above link:
Geolocation
In windows phone 8.0 we had two namespaces with almost identical content, the old System.Device.Location and the new Windows.Devices.Geolocation. In 8.1 only Windows.Devices.Geolocation is left. If you want to update old apps using the System.Device.Location there are plenty of information on the internet. The 8.0 maps api used System.Device.Location.GeoCoordinate but 8.1 now uses Windows.Devices.Geolocation.Geopoint. More on that in my previous blog: Windows Phone 8.1 for Developers – Maps The only other changes in Windows.Devices.Geolocation are two additional classes and one extra property on Geocoordinate:
GeoboundingBox: Represents a rectangle that defines a geographic
area. Replaces the LocationRectangle used in the 8.0 map api
Geopath: Represents an ordered series of geographic points and is
used for example when you create a MapPolygon.
Geocoordinate.PositionSourceTimestamp: Gets the time at which the
associated Geocoordinate position was calculated, and may be
completely unrelated to the system time on the device. E.g. if the
position is obtained from GPS, the timestamp would be obtained from
the satellites.
The final bullet point is the useful one
Thanks
Steve