The period of a pendulum is 2pi sqrt(l/g) for small amplitudes. He’s most probably referring to the order of magnitude you need, not precisely that number.
That one day should be spent with family, friends, taking a stroll, meditating, praying, studying, reflecting, napping. It’s not just the negation of work. Some say it’s an “island in time.”
This has already been solved thousands of years ago and it’s called Shabbat, one day of the week of true, strict rest. No doing the laundry, no cooking, no driving the car. In general, no creative activities which modify the world in some way.