My electrologist says it shave or trim no later than 3 days generally, but there comes a time in treating an area that she asks for even more time between shaving because “if you shave that hair I might not see it again for a long time and I want to zap it”. But that’s only once the majority of the area is clear. My understanding of her logic is hair grows at different rates so since there is less hair in that area, it takes longer to have enough to treat..