If you use a UV protectant spray, then you will want to apply it everyday if you are in the sun. If you're only out for like 20 mins, you probably don't need it. Also, if the UV protectant doesn't contain any harmful ingredients it also doubles as a sealant for extra moisture retention. However, if you are using Friendly/ Resilient silicones in your routine, for example in your conditioner, then these should protect your hair from the sun until you wash them out. These can be quite useful if you are looking for an alternative to your UV spray.