Brothers Become Paralysed When the Sun Sets Each Day (2016)

I wonder what would've happened if they changed timezones, or got taken to a place with 24 hour sun...

Pure conjecture here, but I wonder if it's something tied to their circadian rhythm and melatonin production (a hormone that regulates sleep-wake cycles). In the normal case, the body creates melatonin naturally and its tied to light and circadian rhythm. I can imagine a case where their genetics are such that instead of a slowly ramping production that normally happens, they get a sudden spike? This would also explain why their timings change as daylight hours do as our body's sleep-wake cycles are affected by daylight hours.

Again, pure conjecture, but an interesting case nonetheless.