Should still have something similar to this
Untitled Document which is for MTCA but can't find it anywhere. All my old training docs. are now in a museum
but found this quote
February 1980
The Short-Term Conflict Alert (STCA) tool becomes available. The system provides controllers with a pre-warning of 128 seconds about possible infringements of minimum separation standards.
Times change, you might find more on page 3 of
www.skybrary.aero/bookshelf/books/299.pdf this