What you require is a timer that works in milliseconds (10mS = hundreds, 100mS = tens, 2000mS = 2 seconds)
Then some way of counting them, then some form of a driver for the 7 segment display, etc.
The easiest way i think would be to use a micro processor, as it can do all you require pretty well with one chip.
Depending on how the 12 volt input signal is used you might need to add a opto coupler to isolate the micro from the 12 volts, as micros work on a max of 5 volts.
My choice of micro for this application would be a Picaxe as they are easy to program and no special equipment is needed, other than a computer to download the program from.
There is excellent support for picaxe on the picaxe forum and all the information and software is free to use.
There is also development circuit boards avaliable that you could adapt to suit your needs (check out the Kiwi board)
Pete.