Most of the great cathedrals took hundreds of years to complete. Part of that was due to more primitive technology, i.e. all hand tools, no machines to do the heavy lifting, etc. But another component was the meticulous care taken to simply get it right. No short cuts, no crap materials, no halfass. And that part of the job should still be in effect, if they don't want their repair job to stand out for centuries to come as an obvious flaw on a jewel. So I would be very concerned if the work wasn't going slowly.
