Assuming this is a love spell and you don't want to wait for a more user friendly moon phase you could execute the spell on a Friday . Fridays are always good for love/ attraction/ lust spells. However as I'm sure you're aware these spells are a little unpredictable so wait for a waxing/ full moon if you can.
Opinion is divided on this anywhere between 1 and 3 days. Most agree 3 days after will be ok but you'll have to make that decision. An alternative might be to go for a more long term spell like a honey jar spell which you could work for weeks or even months.