Chang'e 4 is in Moon orbit since December 12, the landing is scheduled for January 3. What is planned during the 22 days in orbit?
The Planetary Society article Chang’e-4 Successfully Enters Lunar Orbit - Next stop: the Lunar Farside speculates that they are waiting for sunrise!
Waiting for the morning
Now that Chang’e-4 has already entered lunar orbit, why is it waiting 20 more days to land? There are probably several reasons.
Engineers have work yet to do to prepare for landing. They will test instruments, test the relay link with Queqiao, and so on. They may need to adjust the orbit in order to better target the landing, which must be more precise on the rugged farside than Chang’e-3’s in the flat nearside maria.
They also have to wait for the Sun to rise in the landing region. The far side of the Moon is not the “dark side”, it has daytime and nighttime as we do. The difference is one lunar day is much longer, with about 14 earth days of daytime and about 14 earth days of nighttime.
You can check to see where it is day and night on the Moon easily at the Lunar Reconnaissance Orbiter QuickMap website. Open up the Layers tab, choose “Overlays,” and then tap the “Sunlit Region” button.
Read the article (and future Planetary Society articles about Chang'e-4) for more details about the landing.