Late 80’s to mid 90’s.
On a somewhat related note, the Pepsi Max advertising team are having a bit of a field day with Coke Zero - at least in the advertising on the Tube. I can’t find any examples online, but they all take the example of a letterbox format ad with a thermometer scale, labelled Zero to Max, and with a picture of something naff at the Zero end and something cool at the Max end, like as a moose and a fox. I love it when two big brands start trying to pick holes in each others advertising like that.
Of course, Pepsi has been referring to its rival by name for years, but I was suprised to discover that the Coca-Cola Company did the same thing in the 1980s. Because the powers that be weren’t willing to give up on it, both the “new Coke”- referred to simply as Coke, not Coca-Cola- and the original- dubbed “Coca-Cola Classic”- were on the market at the same time for a number of years. Coke’s advertising, originally with the “Max Headroom” character and later with other ideas, referred to Pepsi by name.