Expended End Date

If this solution doesn't work for you (it spans the event box till the dotted end):

http://forums.daypilot.org/Topic.aspx/2834/expected-end-date

you can use two separate events (one with the actual duration, one for the expected difference) and disable all actions (resizing, moving, etc.) on the dotted one.

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