It measures and displays wall clock time in millisecond resolution, using the system-provided timer (i.e. with approx 15ms accuracy under Windows, and <1ms accuracy under Linux). This includes the time to load the program as well as any time spent in waiting e.g. for useless live antivirus scanning stalling your computer before launching a program or time passing while e.g. your program displays "press any key to quit" at the end of its execution.
It is therefore very possible that the displayed time is much more than you'd think it should be.
