This logic assumes everyone onboard experiences full utility from every hour of activities, but that simply won't be the case. There will absolutely be parents tagging along who aren't drawn in by the gimmick, as well as kids with short attention spans who'll be wishing for a pool break.
The Starcruiser also doesn't look particularly big, meaning there will only be so much physical content to explore.
I can't be alone in thinking 48 hours of no natural light sounds like a nightmare, barring one brief excursion to Galaxy's Edge. The least they could've done with such a boutique offering is give those inclined an in-theme pool or fitness center, so there's somewhere to decompress when guests are feeling claustrophobic or over it.