I knew in the past question that access to the play tab was added to the development wish-list. Has this issue been resolved in versions 2018R3 and later?
There is a message called SmartClient.GetTimelineSelectedIntervalRequest which can be used to retrieve the current selected interval of the timeline. It was introduced in version 2017R1.
Dear Bien-san
Thank you for your reply. Completed without incident.
Shuhei Ikeda