"Wait 3 days" should mean three days after the message before it. When delays are interpreted against the start of the sequence instead, inserting a new step two shifts everything after it, and a sequence you thought was spaced weekly goes out in a cluster.
Steps now carry an explicit order, and delay_days is measured from the
preceding step. Reorder your sequence, insert a step, or delete one, and the
spacing between the remaining steps stays exactly as you set it.
The duplicate-delay bug that could schedule two steps for the same moment is gone with it.