According to Ahmet Şık, a journalist who was arrested after writing a book that charged the Gülenists with extensive infiltration of the Turkish state, the weekend coup was indeed headed by Gülenist officers who had been planning to stage it before a promotions meeting in August, when they were due to be dismissed. Their plans were discovered, he writes, and they knew they were to be arrested at 4am on Saturday morning. He believes the officers, aware they had been rumbled, decided to attempt the coup early on Friday night. This would explain why the coup was so poorly planned. Consistent with this, Erdoğan has acknowledged he knew of “military activity” at least seven-to-ten hours before the coup.

b_b. This seems fairly consistent with common sense.