Please provide a sample code to write a Custom FormItem to display a dialog

Using v10.0p_2015-02-25/PowerEdition Deployment (built 2015-02-25)

We have a ListGrid and set setShowFilterEditor(true);
The grid has a datetime column. When the column is clicked we are getting a dialog with Start and End Times. I have several questions here.
1. Is there a convenient way of disabling the items that show up in the
dropdowns that alow relative days as input?
2. I did try the following
ListGridField timeField = new ListGridField("time", "Time");
timeField .setFilterEditorProperties(new DateRangeItem());
But it doesn't provide the date and time. Also, this would need
multiple rows display for filter which I don't want to allocate.
3. If we want to write a custom formitem with a custom, would you
please point me to a sample code perhaps? I did look in the
showcase.

Thanks in advance