The longer you leave it between stretches, and the smaller stretches you do, the less painful it will be and the less chance of something f**king up. I've blown out my ear before, its not nice. I'd say leave it at least 6 weeks after piercing, I left it 2, and the first stretch hurt like a bitch, but I did go straight to 4. Another option would be to get it pierced at a higher guage and stretched to 3mm or so immediately after piercing, all decent piercers would do that for you. Don't go to a cheap jewellery store with a piercing gun, spend the extra tenner or so. On 20mm now, and 5mm on the other one, was 6 but I lost my tunnel.