Im trying to do just that, that is build a timer that countsdown accurately to the minute. Ideally this device should have a range of about 5 second countdowns to 36 hour countdown. I'd like to add a 7-segment LED display wired to count as well but Im not sure I think i can do that with a 555 without a crystal oscillator. What im thinking might work is using a crystal oscillator in tandem with a microcontroller that will know the number of clockcycles a second are before decrementing the value on the LED display where at T=0, it should send a high voltage pulse to the output terminals, preferably high enough power such that it can accomodate turning a small dc motor on. Thanks for your help and valuable insight.