How long to cook a 150 lb. pig in the ground?
Last time I did one it was an overnight proposition, sources I find recommend planning on 24 Hours for a 150lb Kalu-a-que. 


  A pig roasted in the ground, Hawaiian or Kalua style, can take 12
  hours if done right and if it is filled with fruits and vegetables it
  can take 16 hours or longer.


If your pig is a purchased commercially (from a local farmer or reputable butcher) internal temps above 145°F are considered 'safe' but some people are still not comfortable with pork that is still that pink...so you should probably aim for 155°F (some will still be pinkish, others will have moved onto whitish, without (hopefully) drying out too much. 

If you are serving up a wild pig/boar... (IMHO) Nothing less than 180°F will do. 

I would recommend giving yourself at least two hours of 'slack' to pull the pig out of the hole two hours before scheduled feed time and start slicing (and storing in a couple of ice chests (no ice...insulated to keep the meat warm) so that serving goes faster. Slicing/chopping 'to order' will create a bottleneck in your festivities.