Yep we are the first to land on the dark of the moon
There's no dark side of the moon as such. Because the moon is tidally locked to the earth, we always see the same side of the moon. This is the
near side. The opposite side which we never see is the
far side.
1 day on the moon (sunrise to sunrise) = ~14 earth days.
So almost every point on the moon will be in the dark for 14 earth days continuously and in the light for 14 earth days continuously. Since the systems depend on solar power to work, timing the landing just as lunar day begins at the landing site would give the maximum mission time of just under 14 earth days/half lunar day.
Once the sun sets at the landing site, temperature will drop drastically, and pretty much freeze and destroy all systems on the lander/rover. If landing it today wasn't feasible, they would have waited a month for the next opportunity.
If you're wondering why everyone chooses to land on the near side of the moon, it is because we do not have line of sight from earth to the landing site for communication. The lander would have to relay data via the orbiter, which would not always be in LOS since it is going around the moon continuosly, so overall bandwidth/transmission time would be severely limited.