From my own experience which is two major rebuilds of private crashed aeroplanes, I'd say potentially rather longer than building one from scratch.
Every part must be treated as suspect, huge amounts of bonding, painting, etc. to be removed and redone (much harder than doing from new). Far greater depth and rigour of inspection and NDT than I'd expect on newly made parts.
You have really got to want that aeroplane. Speaking for myself, although I learned a huge amount from both rebuilds - I'd rather build one from plans (probably including designing it as well) than do a rebuild again.
Costwise - it depends upon how you count the man-hours. At what I normally charge for my time, both those rebuilds cost considerably more than buying a near-perfect second hand aeroplane of the same type.
G