A single plant can stay 4-5 years or more, undisturbed. In the northern temperate hemisphere, they will start to flower from May to late June according to the location where you are living. They will usually follow the beautiful large flowered iris germanicas, but in a totally different style. Each plant will usually flower 2-3 weeks. Fresh flowers open in the morning and they die at night.
New ones open the next morning.
In some warmer areas some varieties may repeat all summer long several times. More the north, less varieties will tend to repeat. There are early, mid season and late varieties, so when combining them you can expect a minimum of one and half month of flowers everywhere. South hemisphere will have their flowering time at the corresponding reverse months. There are varieties for every taste.