https://wccftech.com/world-of-warcraft-classic-demo-playtime/

The World of Warcraft Classic Demo playtime will initially be limited to a cumulative 60 minutes, Blizzard has announced.

Blizzard already stated that they might implement time limits to help as many people as possible play the Classic demo, and this initial time limit is now official. Players who play the demo for a straight 60 minutes will be disconnected from the Demo servers, and will have to wait for 30 minutes before being able to log on again.