Maybe.
Virtual attributes are not store in the database they are calculated on the fly.
One way is to use the same calculation (if you can figure it out) in the query.
Another is to see if the attribute is in a db view, then it can be queried from the view.
See
Reading Calculated Attribute in GEL Script?
Can't say off had about the Gantt if that can be retrieved in either of those two manners.