https://www.gamespot.com/articles/microsofts-xbox-e3-2018-press-conference-length-es/1100-6459535/

How long will the Xbox E3 2018 briefing be? According to Phil Spencer, you should expect the show to run for about 100 minutes. That estimate was based on the company's last run-through. The real runtime could differ, but it should be something in that area.