UKHeliBob:
Set an int variable to the start value, say 10, and a second unsigned long variable to the current value of millis(). This is the start time.In loop() check each time through whether the current value of millis() minus the start time is greater than or equal to 1000. If it is then decrement the counter variable, display its value and save the current time from millis(). Keep going until the counter reaches zero then do whatever you need at that point.
Where are you stuck ?
May you please give me an example of what this may look like?