Biphasic sleep in adults can involve one long sleep bout at night and a shorter bout during the day, timed to coincide with natural drops in alertness.

“coming back to basic sleep I describe one version once we are adults which is the Siesta like notion one long bout at night short bout during the day and that bout during the day is usually matching that drop in alertness that we described it sort of hits that sweet spot right there and it's quite easy for some people to fall asleep in a period between somewhere between one and four 1 to four yeah”

“A biphasic sleep pattern can include a siesta-like nap during the day, typically between 1 PM and 4 PM, which aligns with natural drops in alertness.”

“somewhere between about two to four p.m both you and i will have this kind of drop in our physiological alertness in our physiological level of brain activity”

“somewhere between about two to four p.m both you and i will have this kind of drop in our physiological alertness in our physiological level of brain activity in other words as if as a species we're almost pre-programmed to have this enforced dip in our alertness”