This really means nothing. They neglected to mention how they put mice through the timeshift test.

In anycase, you can take a number of various reasons of how timeshift (with no regards to flying) shortens our lives as well as the 21st century.

For instance, greater amounts of day light and artificial lights decrease the production of Melatonin in the body. Having that said, with numerous studies showing a direct realtion between cancer growth and lack of melatonin production.... that's just a prime example of 21st century life.

The list goes on and on..... no surprise with the mice, but no direct relation to our occupation.