The time it takes for mold to form on dishes can vary depending on several factors, including the environmental conditions and the presence of mold spores. In general, mold can start to grow on food residues or other organic matter within 24 to 48 hours under favorable conditions, such as warmth and moisture. However, it's important to note that not all molds are visible to the naked eye, and they can grow undetected for longer periods under certain circumstances. Regularly cleaning and drying dishes promptly after use can help prevent mold growth.