On September 30, 1581, Nobunaga launched his own invasion of Iga on a much larger scale. The immediate trigger for this second invasion was a visit by two residents of Iga the month before to Nobunaga's stronghold in Azuchi during which the men offered to serve as guides for an invasion of the province. Nobunaga agreed and rewarded the men. By this time Oda was at the height of his power. He controlled most of central Japan, including all of the territories that bordered Iga. He was therefore able to assemble a large army which attacked the province from all directions: 1. 10,000 men under the command of Nobukatsu and Tsuda Nobusumi entering from Ise  to the southeast.2. 12,000 men under Niwa Nagahide and Takigawa Kazumasu entering from Tsuge to the northeast.3. 7,000 men under Gamō Ujisato and Wakisaka Yasuharu entering from Tamataki to the north.4. 3,700 men under Tsutsui Junkei entering from Kasama to the southwest.5. 7,000 men under Asano Nagamasa entering from Hase to the southwest.6. 2,300 men under Hori Hidemasa entering from Tarao to the northwest. Against this large army of 42,000 men, the Iga defenders only totaled 10,000 at most, and these were spread throughout the province. The Oda forces advanced, torching castles, shrines, and temples, and meeting relatively little resistance. The most significant military actions were the siege of Hijiyama Castle, which had become the rallying point for the northern Iga forces, and the siege of Kashiwara Castle in the south. With the surrender of the forces in Kashiwara Castle on October 8, organized Iga resistance came to an end. Nobunaga himself toured the conquered province in early November, and then withdrew his troops, placing control in Nobukatsu's hands.
Question: When did residents of Iga visit Azuchi and offer to serve as guides for an invasion?
Answer: August 1581