Are there more than one Hour Glass limited editions?
Here's another claimed Sinn 1010.5976 limited to 399 which looks totally different again:

Bonhams : Sinn. A Limited Edition Blackened U-Boat Steel Diver's Wristwatch with Date
Model/Reference: U Black, 'The Hour Glass', from a limited edition of 399, 1010.5976 Year: Circa 2010 Calibre: Automatic Dial: Black, signed Case: 44mm, screw back, signed Strap/Bracelet: Black rubber with black PVD folding clasp