ok, were gonna have a timer that will be on until the timer turns its output low. the output of that will go to the motor and goes through an inverter to another timer, which is off until it turns inself on, and the output of that goes to a circuit that stops a high signal after (blank) seconds of pass time. the out put from that goes to the input of the first timer. in theory it will be a timer that you can change the time of the on/off periods. if you dont understand something i said, google it! make the timers with 555s (search monostable multivibrator 555 circuit for info on that), and build your own inverters (search inverter schematic) or buy them. id suggest not using a microcontroller, as this project can help boost your electronic skills.
hope this helps,