Sure thing. Show car glaze has no protection its a glaze.
P21S should last about a month or so ...you can tell if the wax is still on the car when you wash it, if it beads nice and tight you should be ok, if not you should put something on it.
Any of the above should give you at least a month of protection of course it depends on if you car is sitting in a garage or if its your daily.
For more protection you might want to try a sealant like Einszett Glanz or Menzerna FMJ.
I have been told by my customers they see about 3 months with FMJ and 3-5 months with Glanz...