According to the transportation rules, if you are planning to visit the Great Wall in the evening and then go to Wu Town the next day, a joint ticket (联票) can be used. The joint ticket is designed for tourists who want to visit multiple scenic spots within a specific period, allowing them to purchase a single ticket that covers admission fees for all participating attractions.
In this case, as long as both the Great Wall and Wu Town are part of the joint ticket’s itinerary, you should be able to use it to enter these two popular destinations. Please note that there might be some time restrictions or conditions on the joint ticket usage, so it is always a good idea to check with the relevant attractions or transportation authorities before planning your trip.