In an emergency situation, implementation of the change to Runway 08L/26R can be expected to take substantially longer.
Thats the important bit.
Depends on how much notice there is. How many aircraft need to be removed from infringing stands, whether closure can begin with the main runway (RETs blocked) before it’s closed. And lots more.
Too many variables to give a precise estimate but 45-60 minutes or more is entirely reasonable.