It's time travel, so "already happened" is not well defined.

> I wanna see the conference room meeting where they decide to push an unfinished, unstoppable technology. I guess T1 is the closest as it happens when Skynet "gains intelligence"

This is the mid-point of T3. From the Wikipedia plot summary:

  General Brewster is supervising the development of Skynet for Cyber Research Systems (CRS), an autonomous weapons developer. The Chairman of the Joint Chiefs of Staff pressures him to activate Skynet to stop an anomalous computer virus from invading servers worldwide. Brewster fails to discover that the virus was Skynet becoming sentient. John, Kate, and the Terminator arrive too late to stop him from activating it. The T-X appears, fatally injures Brewster, and controls weaponized CRS T-1 and HK drones to kill other employees.