No, never cover a wet painting. It's important to let paintings air dry regardless of the medium. Anything covering a wet painting will create a risk that it gets partially stuck to the paint surface as it dries and will damage the painting when you try to remove it. Simply make sure that where you leave your paintings to dry is dust-free and has good ventilation. Depending on the medium, indirect sunlight is also helpful. Direct sunlight usually is not recommended for long periods of time.