Because I use Winsor and Newton Alkyd Fast Drying Oil Paint, Liquin and white spirit, while painting very thinly, I need only wait a week, however, regular oil paint using slower drying mediums and perhaps painted more thickly requires much longer and can also be effected by temperature and humidity, which will require six-months to one-year. It is important to remember that paint film dries from the inside out. It might appear dry to the touch but still be in the drying process. Acrylic paint typically dries within a few minutes. Some people actually use a hair dryer to speed up this process.