The drying time of canvas panels depends on the layering, thickness, humidity, and temperature. Paints normally dry in 10-30 minutes. They may, however, take several hours to fully cure. Thick layers may take a day or more to dry. Use thin layers and work in an open space to speed up drying.
Let the mistake dry completely before attempting to correct it in a painting on canvas boards. Then, using the desired color or background, paint over it. For bigger mistakes, lightly sand the area and apply gesso to prime it again. Some paints like acrylic have tolerance and allow for layering, so with patience and care, you can often blend in changes seamlessly.
Yes, artists canvas boards can be reused. Clean the canvas boards frames thoroughly, removing all traces of old paint. To create a new surface, you may need to sand or prime it. After cleaning and preparing it, you can re-paint it with acrylics paint or another compatible medium.