Daylilies, sedums and irises (flowering right now)?
You can certainly divide Daylilies and Sedums right now but Irises that are divided in the spring usually don't bloom that year. I have heard 6 weeks after blooming they are okay to be divided.
Generally, it is not a common practice to divide anything that is still flowering. Some plants can be divided soon after flowering. Waiting six weeks for your irises seems to be good advice to me.
I divide my irises the end of June or beginning of July, after flowering. This gives them enough time to set a healthy rootsystem by fall. Sedums I divide in the spring. Marg