Very strange. I cant think any other way. A possibility is (although very rare) to read the time via WMI calls. But that makes the application compatible only with XP/2K, since the WMI is available to Win98 only if the WMI Core is installed. Have you checked if it reads the time of system files, maybe via GetFileTime? Have you done the test to set the clock forward to see if detects it and kills the app? If yes, then the trial system is time comparable. If not, then its sounds like timer (GetTickCount).

Why you dont share with us the name of the application?