Credits goes to Shalashashka who posted that in another forum
while connected to xbox live, play the game for once a day for 100 days - to get this go to your dashboard and choose console settings. select clock and then time zone. change the time to -12 hours then load the game, press start, then choose chapters. exit back to dashboard and change the time zone to +14, load the game and press start, select chapters press a, exit back to dash. keep doing this to gain 7 days. basiclly you are using the world time zones to change the date on your clock. ist should take about 1 mimute to get one day. i got this after 75 odd tries rather than 100.