Product review (5 stars): Fixed my dryer.  Read for a troubleshooting tip.
Fixed my dryer issue.  This is not the easiest part to diagnose, a proper diagnosis requires using an ohm meter and testing the switch positions using the logic diagram from the manufacture, but one way to tell if the timer is bad is to disconnect, remove from the dryer and shake, if you hear anything rattling then it is most likely the source of the problem.  A working timer will not make any noise when you shake it.  Take pictures of the wires before you disconnect, most are labeled on the timer but its easier to look at a pic and connect the wires than trying to read the small letters indicating the wire color that are molded on the timer.