Assuming your solar panel lights have a full charge in the battery, you can expect them to stay illuminated for many hours. This will depend on the type of lights you have, as different types and brands may have different performance and also the type of battery installed within the lights.
If you are looking for averages, a standard type of solar path light – those that are usually on stakes in the ground – could give you as much as 12 hours on a full charge. This will be when it has been fully charged by the sun’s light for a full day.