There is no magical formula to tell you exactly how long chkdsk will take to run. Chkdsk times are dependent on the number of files and the extent of the corruption. Chkdsk time is not relevant to the volume size... although the number of files does commonly increase with volume size.
The best recommendation is to upgrade to Win2012 or higher, there has been significant improvements to chkdsk and your downtime will go from weeks to seconds to run chkdsk.
Thanks!
Elden