The software giant had previously promised that the Windows 7 RC, which is available now for free, would work until August 1, 2010. However, the company plans to take a heavy-handed approach to encouraging people to upgrade to the full retail version from next March.
"For the RC, bi-hourly shutdowns will begin March 1, 2010," said spokesman Brandon LeBlanc. "You will be alerted to install a released version of Windows and your PC will shut down automatically every 2 hours.
"On June 1, 2010, if you are still on the Windows 7 RC, your licence for the Windows 7 RC will expire and the non-genuine experience is triggered," he added, warning Windows 7 RC users that at that point, the copy will be marked as bogus, with on-screen nags and a black background.
With automatic shutdowns due to start on March 1 2010, those who have downloaded the Windows RC have ten months to play with the OS before it starts to pester them to upgrade.
That puts Windows 7 on a similar pre-release schedule to Windows Vista. In 2007, Vista RC1 and RC2 started rebooting on June 1, nine-and-a-half and nine months, respectively, after they were released.