Bull6791- FWIW, my guidelines for "when to reapply" are:
1) before it needs doing. Stay one step ahead by re-LSPing every now and then even though it's obviously not necessary. If you use something really quick and easy (e.g., SprayLSP as a Drying Aid) you can keep a car "just waxed" with hardly any time/effort at all. Like...a few minutes.
2) whenever some characteristic that you value changes. I go by water behavior: if the beads/sheeting change, if the water doesn't blow off as easily, if contamination doesn't wash off as easily as usual, etc. etc.
I often use a combination of those two approaches. I apply something very durable when I do a Big Detail (like you're about to do). Then I maintain that by using the SprayWax as my Drying Aid.
If you use the Collinite 845 (which I still keep on the shelf but seldom use), Meguiar's Ultimate Quik [sic] Wax or Optimum Car Wax would be great for the Spray.