When did inhabitants use the first tools in the Indus Valley? The Neolithic Period (6500-4500 BCE) period? The Chalcolithic Period (4500-3500 BCE) period? The Bronze or Indus Period (3500-1800 BCE) period? Or 2 million years ago?
Only 20% of the 1,573 respondents to this poll got it right - 2 millions years ago. As Mark Kenoyer writes in Ancient Cities of the Indus Valley Civilization, "The earliest inhabitants of South Asia belonged to the hominid species Homo erectus, the ancestor of modern Homo sapiens. These stone tool-using hominids lived in the Potwar plateau region of northern Pakistan over two million years ago where the oldest stone tools have been discovered near the town of Riwat. Most of the Stone Age or Paleolithic sites in this part of the subcontinent, however, date to a much later time, between 30,000 and 10,00 years ago. Cave sites, such as Sangao, and temporary camps of Middle Paleolithic and Upper Paleolithic hunters and gatherers have been found along the eastern edge of the Saraswati River in Rajasthan and Gujarat and in the highlands of Baluchistan and Afghanistan to the west of the Indus river" (1998, p. 33).
Indeed, there is also evidence for pre-Homo sapien use of tools at the Rohri Flint Mines in Sindh near Mohenjo-daro, which were also used during the ancient Indus period.
Many articles on the site by Paolo Biagi who has studied prehistoric hominid activity in the area in great detail give some sense of the depth and variety of this activity at https://www.harappa.com/category/article-author/paolo-biagi.