Some people have used 14 days for copper treatments, but I've found that to be too short of a time. At the very least, you need to treat for 14 days beyond the date of the last fish added to the group, or the last date any symptoms were seen (21 days is safer though).
For ammonia control, you need to test the water and keep the ammonia below 0.50 ppm (0.25 is best) through water changes or the addition of beneficial bacterial. You can't just rely on a set amount of water changes because ammonia builds up at different rates in different tanks.
Jay