Gloria Mark said it in an interview in 2006.

For a lot of us that would definitely count as a source. They seem to be credible, they seem to be quoted in a credible media outlet, they seem like an experts on the topic, they seem like they're talking about a real and specific piece of research. So I think that would count for a lot of us. But for purposes of this particular article they're looking for a printed primary source of the research itself rather than a quote about it.

	▲	didibus 4 days ago \| parent [-]
		> When people did resume work on the same day, it took an average length of time of 25 min. 26 sec (sd=54 min. 48 sec.). From the Gloria Mark paper: https://ics.uci.edu/~gmark/CHI2005.pdf That's the paper source. And the researcher when interviewed verbally gave a slightly different number in the same ballpark of 23 minutes and 15 seconds instead of 25 minutes and 26 seconds.