When to go in varies so much on the paint. For us, we can get 4-5 years out of Trinidad SR even though we average 7 months on the hard. The
lift operator suggested not
sanding before re-launch. (It was pressure wash cleaned on haul-out.) We tried it...no change in performance. The oxidized/sun exposed outer coating ablates leaving the copper loaded antifoulant hard coat to do its work
But for our PropPurr™ prop coating, the manufacturer recommends that the
boat be launched within 1 hour to 2 days. In the water, there is less oxygen and the water is surface tension "repelled" by the silicone coating. In the air, the oxygen can penetrate the coating (like moisture vs. water in the Gore-tex rainwear), eventually leading to
corrosion below that compromises the silicone coating.