The phrase "a long presentation" is correct and usable in written English.
You can use it when describing the duration or extent of a presentation, typically in a professional or academic context.
Example: "The conference featured a long presentation on the latest advancements in renewable energy technologies."
Alternatives: "an extended presentation" or "a lengthy presentation."
At one board meeting, Ellis writes, "a long presentation was being made that was overloaded with dull, detailed statistics.
He spoke at the start of a tour of the Center for Genetic Engineering and Biotechnology in Havana, after a long presentation on Cuba's biomedical and genetic research.
If you let on your ignorance, most owners, rather than sneering, proudly launch into a long presentation about their wines, their grapes and their history.
The company's technical director gave a long presentation packed with graphs and data which he claimed backed up the Russian manufacturer's results, but did not address why so much eyewitness evidence put the Buk missile system inside separatist territory.
Mrotz was sympathetic to Omar, and gave the candidate and her staff a long presentation that mentioned ways that progressives could express criticism of Israel without inviting charges of anti-Semitism.
In a long presentation to SoftBank's shareholders, Mr. Son argued that his proposal would increase his company's debt to three times earnings, while Dish's would raise its and Sprint's to nearly six times earnings.
In an appearance at an auditorium at Keene State College, John Kerry was into the 30th minute of a very long presentation when one of the young campaign volunteers standing behind him, Patrick Doyle, 14, collapsed under the hot klieg lights.
However, it is a relatively long presentation, perhaps two or more minutes (at least that is how long it felt).
The first part of a recent showcase in Budapest, Hungary was a 30-minute long presentation of the D3X, comparing the D3X to the D3.
Most had come to hear Huanming Yang, the B.G.I. chairman, deliver a long, emotional presentation that included a PowerPoint display with ninety-one slides.
Mr. Eischied said he was not responsible for various documents, including a long written presentation by a "champion" seller of KPMG tax shelters titled "generating capital losses".
