Timer circuits are handy where you need to switch on or of devices after some time. You just set timer and start. After time elapses microcontroller sends signal to relay and toggles its state. Adrian have built really simple and obvious version of such device.
For this he used old good Atmega8 microcontroller, hooked up couple seven segment LED displays. There are enough I/Os on AVR so they are connected directly and no special circuits like transistors are needed. For set and start there are two push buttons. When time runs out microcontroller switches relay and also sounds a buzzer.