Uber is a 24/7 service, whenever a driver is online, you can hail an Uber car. Usually, there are mutliple drivers online 24/7 for medium to large cities.
Is Uber cheaper at 4am?
Uber surge pricing is not based on time of day. It's calculated using a strange blend of math, metaphysics, and alchemy. But seriously, it's based on supply and demand. If there are more people looking to request a ride versus the number of drivers available, the prices go up.