OP misquoted the article. It’s 819m hours, not 819b. A rough estimate of the average number of internet users was 3.6b over that period rather than 8b, hence the ~450x discrepancy.

819m / 3.6b / 13 / 365 * 3600 = .1726 (rounded to .175 for a cleaner number)

It’s over a 13 year period:

The researchers took the average completion time of 3.53 seconds across both image and behavior CAPTCHAs and multiplied that against a low-end estimate of 512 billion v1 and v2 reCAPTCHAs completed across the internet between 2010 and 2023, resulting in the following estimations of their impact on our lives:

It ends up being like, .175 seconds per day for the average internet user after some rough estimates