How can I change the sequence to overlap the timeitem? Now the timeitem that begins before is in top to the strip of the overlapped timeitem. Can I choose the order with that superimpose the item in case of collision ?
The CollisionDetection places early time items in the highest position. The way it does this is by assigning a non zero value to the SubCol property of the TimeItem object.
If the Owning GanttRow has SubColumns<>0 then the row is divided into sub rows (they are called sub columns for historic reasons and its a good name when the gantt is in the ScheduleMode) time items with a non zero value less or equal to GanttRow.EffectiveSubColumns will be draw in the sub row corresponding to that number.
So if you want to have the time items the other way around (early time items in a lower position) you can change the SubCol property after or in the OnCollisionDetect event.