The first Scottish machine, D6138 went to Edinburgh St. Margarets in February 1960, Kittybrewster examples following shortly after.
Between April and September 1960, the original 'pilot' examples, previously working in England, were transferred to Glasgow Eastfield Depot (followed by all subsequent production machines). After various repairs and 'improvements', crew training between Glasgow BS and Dundee had commenced by January 1961, the engines running in pairs.
The short answer, is spring 1960, with Kittybrewster employing them on GNoSR lines.
Hope that helps.