If you mean what time they stop delivering, they deliver up until 10 PM or until all the packages have been delivered. if you're referring to the office where you can drop off a package, the hours are posted on the door. if you're referring to having a package picked up, you can make arrangements by going to ups.com and create an account 24/7.
UPS does not stop working. This is because they are always shipping parcels from one place to another. However, the offices close and the end of business in the evening. If you are talking about the UPS for computers, then it stops working when you switch it off.