Why is timing belt called "timing" belt?

The timing belt is related to the intake/exhaust valve timing and the ignition timing. If the belt is going to fail soon, the timing will be off. That is the cause of several symptoms. Engine hard to start is one of them.

http://www.ehow.com/about_5875812_symptoms-timing-belt-failure.html

 

Failure Symptoms

• There are several symptoms of a worn or frayed timing belt. Be sure to see your mechanic if you experience rough idling, difficulty in starting or hear strange noises coming from the engine. As with many automotive problems, see your mechanic at the onset any of these symptoms. Delaying that inevitable trip to the mechanic will more than likely make the situation worse as the miles go by.