Here is a link that might be helpful for you in determining the time going into in case you haven’t already repaired an older quilt. I’ve never repaired one so can't tell you from experience the time involved but found this link that might be helpful for you.
http://www.quilthistory.com/repair.htm I skimmed over this quickly without reading all of it and it does mention that a lot of time goes into repairing a quilt. I guess that really depends on the damage and how extensive it is. I’ve also heard of an ‘honest’ patch, that is when no effort is made to match the damaged fabric.