I had a similar situation to the person you replied to and it wasn't bad.
I took a project with ~20 top level dependencies and around 5k lines of Python / Flask (plus a lot of tests). I YOLO'd upgrading everything to their latest versions in 1 shot including Python 2.7 to Python 3.7, Stripe API versions and everything.
I did that around 2.5 years ago and it took around 45 minutes. The app was using SQLAlchemy, Celery and had a bunch of things you'd expect to see in a SAAS app (users, custom admin, payments, custom CLI commands, migrations, etc.).
I took a project with ~20 top level dependencies and around 5k lines of Python / Flask (plus a lot of tests). I YOLO'd upgrading everything to their latest versions in 1 shot including Python 2.7 to Python 3.7, Stripe API versions and everything.
I did that around 2.5 years ago and it took around 45 minutes. The app was using SQLAlchemy, Celery and had a bunch of things you'd expect to see in a SAAS app (users, custom admin, payments, custom CLI commands, migrations, etc.).