The length of time to boil a deer antler for a knife handle depends upon the antler. You will want to check it often to make sure you don't over boil it. You want the pith in the antler to be soft. Boiling too long results in a brittle antler. If you have the time and patience, try using spring water or rain water to soften the pith. This can take a month, but there will be no fear of drying out the antler.