An entry might have the term early (or very early), mid, mid late, or late (or very late) listed as the bloom time. These time definitions may vary with your growing region. Early generally refers to soon after the snow has melted. For my area, early is generally around mid-March to April. Mid blooms when spring tulips and peonies are blooming, but again varies with the area. Late comes in the early to mid summer. Most bloom stalks with last for several days to a week or more. If you have planted varieties where some bloom during all parts of the season you can have iris blooming from early spring to late summer.
Rebloomers are iris that bloom in the spring and again in the late summer to early fall. Not all rebloomers will consistently rebloom in all areas. If you really want your rebloomers to bloom in the fall, it is best to fertilize after the first bloom is over. In the mild climate of the southern Oregon coast where I live, I have had rebloomers sending up stalks from October to December and blooming into January if we don't have heavy frosts.