An opaque cover will block the UV in sunlight and have the chlorine last a lot longer. The colder water temperatures also slow down all chemical reactions including those that use up chlorine. In my own pool that has a mostly opaque electric safety cover, my chlorine loss rate with no bather load is around 0.7 ppm FC per day at 88ºF (with bather load and opening the pool every day for 1-2 hours the loss is closer to 1 ppm FC), but at 50ºF over the winter this drops to somewhat less than 0.1 ppm FC per day (about 1 ppm FC every couple of weeks). This is with the FC at around 10% of the CYA level and the CYA at 30 or 40 ppm (depending on season) though it gets diluted from winter rain overflow that I intentionally do (pool pump on cover pumps water into the pool and overflows from under the cover to an overflow drain.

If you truly have an opaque cover, then you should not need to have your chlorine start out that high if the water temp is cold when you close in winter and when you open again in spring. Usually, people only need to do that if their cover is not opaque because sunlight will continue to break down chlorine. Note that sunlight breakdown of chlorine is independent of temperature so having an opaque cover is important if one isn't going to be adding chlorine over the winter and wants to open up the pool algae-free.