I can add one small data point to Hyder's time zone history. In 1974, my brother and I took a road trip. Part of our itinerary was the Stewart-Cassiar Highway. On July 5, 1974, we walked from Stewart, B.C. across the border to the First Chance Cafe in Hyder, Alaska, no more than a mile. According to my brother's journals, Hyder was using PDT, just like Stewart.