Another option is to use the "event versions" feature:
http://doc.daypilot.org/scheduler/event-versions/
It will let you define an event version that will be displayed above the event. It can have a custom start, end, color, text, CSS, etc. It can't be moved or resizes. You can use it to define the expected duration. There can be more than one version of the same event (e.g. for all previous plans).
See also a demo here:
http://javascript.daypilot.org/sandbox/scheduler/eventversions.html