The step duration of operations has problem if configuring escalation in action. (Configuration=>Actions=>Create action=>Operations=>New)
Below explanation is based on the documentation: https://www.zabbix.com/documentation/3.0/manual/config/notifications/action/operation:
Step duration - custom duration for these steps (0=use default step duration). Several operations can be assigned to the same step. If these operations have different step duration defined, the shortest one is taken into account and applied to the step.
But in my test, it didn’t use the shortest one if setting one of the step duration to default(0).
Please check the attachment.