97 camry -prestone radiator cleaner-freeze problem

I need to flush cooling system. the only problem is that i have let this go and the outside temperature is in the 50-40 (fah) in the day and 40 to 25 at night. Prestone requires that you flush and drain radiator and then put water and 1 liter of cleaner in and then drive it for 3-6 hrs over a two day period. Will the mixture of cleaner and water be enough to prevent engine block freezing? thanks in advance.