Pip: Pip uses wrong date for DEPRECATION: messages

Environment

• pip version: pip 20.2.3 from /home/di76gum/.local/lib/python3.5/site-packages/pip (python 3.5)
• Python version: 3.5
• OS: Ubuntu 16.04.6 LTS

Description

On 9 September 2020, I ran
python3 -m pip install django2-resumable
and obtained the following message:
DEPRECATION: Python 3.5 reached the end of its life on September 13th, 2020. Please upgrade your Python as Python 3.5 is no longer maintained. pip 21.0 will drop support for Python 3.5 in January 2021. pip 21.0 will remove support for this functionality.

Expected behavior

Since the end of life is still in the future, I would expect the message to read "Python 3.5 will reach the end of its life on September 13th, 2020" instead.
How to Reproduce

Run
python3 -m pip install django2-resumable
before September 13 2020.

Output
DEPRECATION: Python 3.5 reached the end of its life on September 13th, 2020. Please upgrade your Python as Python 3.5 is no longer maintained. pip 21.0 will drop support for Python 3.5 in January 2021. pip 21.0 will remove support for this functionality.
Defaulting to user installation because normal site-packages is not writeable
Collecting django2-resumable
Downloading django2-resumable-0.1.1.tar.gz (7.6 kB)
Requirement already satisfied: Django>=2.0 in /usr/local/lib/python3.5/dist-packages (from django2-resumable) (2.2.7)
Requirement already satisfied: pytz in /usr/local/lib/python3.5/dist-packages (from Django>=2.0->django2-resumable) (2019.3)
Requirement already satisfied: sqlparse in /usr/local/lib/python3.5/dist-packages (from Django>=2.0->django2-resumable) (0.3.0)
Building wheels for collected packages: django2-resumable
Building wheel for django2-resumable (setup.py) ... done
Created wheel for django2-resumable: filename=django2_resumable-0.1.1-py2.py3-none-any.whl size=12304 sha256=163a94d95b4941ecc959f2022c8bf23633ddf99fe00e058de184322d2a56bcd2
Stored in directory: /home/di76gum/.cache/pip/wheels/7d/1d/a4/a94e57629412fe6425c84fb42b24d4d3ffc85e53e9cd096cc9
Successfully built django2-resumable
Installing collected packages: django2-resumable
Successfully installed django2-resumable-0.1.1