The text says 24-60 hours, but then in the table where they talk about the other studies being considered, a lot of them did 48 hour minimum and as much as 96 hours for some. When I saw the headline I was excited because a 16-18 hour fast really isn't very hard for most people, but 48 hours sounds a little rough. I guess if it's just a one-off event while you're doing chemo it's not that bad, but I'm not about to fast 48 hours once a week for the rest of my life.

Other commenters have given the 24-60 hours figure, but it's also worth seeing the section "From animal models to the clinic": "may also mean that humans need to fast for a (much) longer period of time than mice to obtain the same benefits".

And worth noting, it helps in conjunction with chemo

I found the answer by reading all the way to page 2 of the article: 24-60 hours.

Paper says 24-60 hours.