Perhaps my best point of reference so far is that he demonstrated some of his technology at the Westinghouse exhibit at the 1893 Columbian Exposition, which ran from May 1 to Oct. 30th.

I see the possibility of the demonstrations happening between 1889 and 1893, the period during which Edison & Westinghouse were competing hardest for their respective technology's adoption, leading up the Columbian Exposition and Niagara Falls Power Company's adoption of AC.

I'm also finding that they could have happened sometime during or after 1903, possibly in response to the Jan. 4 electrocution of Topsy the elephant, which Edison used as part of his anti-AC campaign. The film was released later in 1903, but I don't know whether the news of the event or the film's release would have had more impact back then, as film wasn't a widespread thing yet.