Humans have a remarkable circadian rhythm that does a pretty good job at defining a day as “24 hours.”

There were experiments with forced desynchronization of human circadian rhythms.

http://www.chronobiology.ch/wp-content/uploads/publications/...

They were very limited, though. We do not really know what would happen on a spaceship that changed its day to 100 000 seconds and subjected the crew to this cycle for months or years.

Given how adaptable people usually are to external influences, I would guess that some adaptation would take place.

To my knowledge, once you take the sun away, it tends to drift more towards 25 or 26 hours. And that's in humans who experienced the externally imposed 24 hour cycle for decades before participating in a short experiment, not potential spacefarers born onboard of stations or ships.