I'm using the .NET sdk, but an answer for the Java sdk could also be
helpful.
Setting the EstimatedStart/Finish doesn't work:
var task = new Borland.StarTeam.Task(cr.ParentFolder);
task.Name = "Name";
task.Notes = "Notes";
// task.EstimatedHours = 4.0; // readonly property
task.EstimatedStart = DateTime.Now;
task.EstimatedFinish = DateTime.Now.AddHours(4);
task.Update();