Eventually you will want to something special with the counter, such as ring a bell when it reaches 31, display letters, flash when it reaches zero or turn off when not used for 20 seconds.
The best thing to do is use a PIC chip such as PIC16F628A. There are lots of information on the web about this microcontroller and I have a number of counting programs that will do all sorts of interesting things.
You just need a single chip, a few transistors and resistors as well as 7-segment displays.
Colin Mitchell
TALKING ELECTRONICS.com
talking@tpg.com.au