When NOT to wax. The day before a surprise shower
Spent most of the day yesterday waxing the Cougar hoping to put the cover on today. Weatherman said 4 days of good weather. Woke up this morning to discover it had rained overnight. Guess I'll be doing the Mr. Miyagi again today before putting on the cover.
To answer the OPs question, I wax at the end of the season to remove any oxidation that's occurred. Then again at the beginning of the season to protect the finish. During the season regular washings with Meguirar's Ultimate wash and wax.