Or, what's more likely than a grand conspiracy: A couple of guards taking on extra shifts are lax in their duties, fall asleep and falsify the records so they don't get caught sleeping on the job and collecting that nice payday. They've probably done this before and it was fine, so what could go wrong here? Epstein, facing the end of his lavish lifestyle and knowing what happens to child rapists in prison, sees that no one is checking on him and decides to hang himself.
I've worked in inpatient hospitals with secure units before, this kind of laziness is not uncommon. Even in jails and youth detention, where residents are checked on every 15 minutes (Q15), 30 minutes (Q30), and hour (Q1) depending on their risk, this still happens. As for the video, I've also seen how crappy these systems can be. Most are old, unreliable, and rely on the deterrence of possibly being recorded rather than 100% coverage.
Sure, it's suspicious and needs to be investigated, but there's a much greater chance that this was due to incompetence than it was maliciousness.