2.5 hrs this morning start to finish, including the hoovering, 4 new cords, even put some mastic in .... just needs a lick of paint tomorrow.if you are going to the trouble of opening up the sash pocket it is just parsimonious to not replace the (relatively cheap) sash cord, especially as the redecoration of the window will cost more than qnit of cord should the old cord break in 6 months time.
Can't be done much faster than that ?