A lot of games on older consoles such as the NES, the Megadrive/Genesis, and even in some cases the Playstation, have their speed defined by the video mode they are played at. This is because they are programmed to elapse a certain amount of game time in one frame, so when the frame rate changes, so does the speed.
This timer helps to see what the current game time is for three situations. Emulators run at full speed which is 60fps. NTSC is marginally slower - one second slower every 16m40s. PAL and SECAM run at 50fps and so are significantly slower.
Bear in mind that many games do run at full speed on all video modes, and all that changes is how choppy the motion appears.