On birth control, how long should I wait to have sex?

I've been on birth control for about two years now. I got a new prescription today but had to go to the pharmacy to get a months pack since I have to get my birth control through mail. Instead the pharmacist gave me a generic version, so I'm most likely going to switch to that. How long should I wait to have sex since its a generic version and there has been no delay between this months pack and last months?