It's actually the norm for post-production to take a much longer time to complete than the actual shooting. Most of the things we see in a single shot are actually perfected in the post-production phase. Besides editing the clips together, there are also lots of things to key out such as the wires, and lots of backgrounds to add in on the green screen. Just keying out the wires for a single episode may even take weeks since the characters fly around a lot.
Then besides the technical stuff like color correcting and adding special effects to the video, there is also the dubbing part which sound editors will need to edit so that the audio is clean. But before the sound editors can do that, the actors need to do the dubbing first. And just like filming, the audio recording process is the fast part. Editing audio is super time-consuming as well. After a long process of editing, they gotta add the clean dubbing to the edited episodes. Oh, and not to forget music and sound effects.
And then there's more. Since C-dramas often come with hard subs, that means they gotta burn those subtitles into the episodes once the videos have been edited along with the audio . They can probably skip the transcription process since the final script needs to be ready for actors to do dubbing. I'm not sure if they use some AI software to autogenerate the subtitles, but even if they do, there's bound to be errors. So they might do quality control and manually edit the spelling errors or out-of-sync timecodes. But compared to video and audio editing, hard-coding the Chinese subtitles probably takes the least amount of time among the three.
What I've covered is probably less than half the things they need to work on in post-production. Pretty sure there is a lot more technical stuff involved in each editing stage. But this is as far as my knowledge goes so I'm afraid I can't share more about the rest.