At what point should one start contributing to open source?

Please don’t feel pressured to contribute to open source if this is not your thing – I see it more as an opportunity to learn and “give back” but it is certainly not a “duty” :).

… small tasks like fixing typos […] time could be spent learning instead

I’d say it depends. I think contributing to open-source projects shouldn’t be all about personal benefits, and expanding/fixing documentation where it is useful is also valuable for a project. Eventually, it is up to you where you want to be on the spectrum between “how does this benefit me personally” and “would this help the community and the people who put so much effort into the things that I am using daily for free.” – it’s certainly not a black or white decision, and there is no right or wrong :)

Btw. depending on your experience level, “fixing typos” can be a valuable learning experience as well. For instance, doing “data science” is not only about analyzing data, but communications skills and team skills are important as well. If you are not familiar with version control, see fixing typos as an opportunity to learn about it or practice working with certain frameworks/workflows.