The problem of apt has trouble me for a long time. 我曾为此换到阿里云的镜像，但是不如清华的快。
Several weeks earlier, I found the problem root from ipv6：
mirrors.tuna.tsinghua.edu.cn 是自动解析，可能清华的镜像发现我是校园网，就以为我有 ipv6, 然而我并没有（此处鄙视南开校园网），所以就等、等、等 1，直到超时。
So the solution is to use
mirrors4.tuna.tsinghua.edu.cn instead of
mirrors.tuna.tsinghua.edu.cn when you can not connect to IPv6 (Especially inside NKU_WLAN):
sudo sed --in-place=.bak 's/mirrors\.tuna/mirrors4.tuna/' /etc/apt/sources.list
Then I get into trouble when I handle docker mirror. That lead me to find a better solution:
sudo apt -o Acquire::ForceIPv4=true ...
By the way, I successfully add deb repository for VSCode, slack, chrome, skype, sogoupinyin. Though it took me 2 hours and more, I thought update software automatically would benefit me a lot.
I think now I should have sloved the problem completely.
0% [Connecting to mirrors.tuna.tsinghua.edu.cn (2402:f000:1:416:101:6:6:178)]
Ign:6 https://mirrors.tuna.tsinghua.edu.cn/CRAN/bin/linux/ubuntu artful/ InRelease