It really does depend on the conditions in your area.
Time of year, how much rain, how much you drive it, is it garaged, all play a part in how durable a sealant/wax will be.
What I would say, is that UPP is so easy to apply and remove - so if you apply a layer say once a month, you shouldn't have to worry about the durability thing. When you see and feel the effect of UPP on your paint, you'll won't want to wait too long before you add another layer!