Different computers have different display refresh rates. The most common refresh rates you'll encounter in the wild are 50Hz (=20ms display frame duration), 60Hz (=16.67ms display frame duration), 75Hz (13.33ms frame duration), and 100Hz (10ms frame duration). Displays running at higher rates (120Hz, 150Hz, 200Hz, etc.) exist, but are relatively rare still.
When you have stimulus timings in /stimulustimes such as
/stimulustimes = [0=prime; 100=target]
Inquisit will automatically determine the closest frame available given a system's refresh rate. I.e., for a display running at 50Hz, 100ms amount to 5 display frames (5 x 20 = 100); at 60Hz, the closest frame is the 6th (6 x 16.67 = 100.02); at 75Hz, it's the 8th (8 x 13.33 = 106.64), and at 100Hz, it would be the 10th (10 x 10 = 100).
That is stimulus durations of approximately
, though not necessarily exactly
100ms are achievable on practically all systems you'll encounter.