May appears to bring low RVP and the start of "summer gas".
IIRC "winter gas" ends around March 15, as far as specially boosted RVP to help cold starting. So in spring and fall, "anything goes". I would watch for a price jump May 1 to coincide with tighter regs and therefore don't share your enthusiasm for "summer gas."
If you're looking for the end of oxygenates (ethanol), your odds are slim to none though.