Best Case 3-5 days, worst case 12-15 days. After that either the business will never reopen until it is reconstructed and or the population (and it workers) will have been relocated and /or in Camps. I still plan for 30 days plus just to be on the safe side. Strangely the Canadian Government say 3 days is enough, but I think they are being a little hopeful and or assume that having everybody with three days of food is better than none.