Hour Angle is measured in degrees, not hours. As I said, it's just like change of longitude, but projected out into space. You can convert hour angle into time difference by dividing it by 15, but it then becomes called arc/time difference, not Hour Angle.
I think that you may be confusing Hour Angle and either arc/time difference or Standard Time Difference (STD). There are some STDs greater than 12 hours. For instance, Chatham Island keeps a STD of 12 hours and 45 minutes ahead of UTC (which is, for all practical purposes, the same as GMT).