Game Clock is Different
The odds are heavily stacked in favor of the PCs. Custom creatures like PCs have an increased feat acquisition rate and PCs can reliably depend on their reserve points to heal them and depend on their save points and strife to protect them. More than that though, they can consistently roll near a 10 any time they have to roll 3d6 to reach a Target Number (meaning they get low rolls less often and get critical threats just as often), and they have massive agency to dictate their own odds of success with Pressing their Luck, Called Shots, Action Points, Awesome-Marks and Skill Advantages, all while the GM almost never rolls anything because the players roll all the dice. For these reasons and more, the players can handle a much tougher challenge just as easily, so all challenges should be created as though the desired CR was one step higher than normal. That means the awarded XP is on-par for their level even though the challenge itself was one step above their level.
Hyperion Voyages is also balanced on the assumption that the game is run on a much smaller in-game time frame and uses villains that express their timetables in days instead of weeks or months. A party might have 8 to 16 encounters in a given 24 hour period. For this reason and others, caster archetypes and other characters that require a night’s rest to recharge have to plan their daily allotment and use their energies very carefully even though they can potentially use those energies many more times per day thanks to short-term recharge methods.
Manage the game clock by keeping track of individual combat rounds as 6 seconds each. Keep track of time spent in in-character conversation with a stopwatch. Assume that the in-character time spent talking out-of-character conversation about player abilities really happened during downtime each night before bed. Keep track of how much time is spent in travel (even between other locations in a community) or asleep. Try to minimize in-combat talking between players about tactics specific to that combat (talking may be a free action, but odds are other PCs can’t hear you in detail over the din of battle).
The hours of daily rest sufficient to recover personal energy (such as spells) must take place within 3/2 of the number of hours of the normal requirement from start to finish, and some 3/4 of that normal requirement must be spent in consecutive rest. For example, a standard 8 hours of rest must take place within 12 hours (12 = 3/2 of 8) from start to finish and some 6 hours of that must be consecutive rest (6 = 3/4 of 8). Interrupting sleep means adding one additional hour of sleep onto your normal requirement.
Generally, the smallest increment of rest which counts towards a daily rest is 30 minutes.
GMs should be well aware of what happens to characters that need sleep but go without it. As seen in the entry for the Appalling Fecundity sign; Elder Evils page 9:
“A living creature can go without sleep for a number of days equal to its Constitution modifier (minimum one). Thereafter it is fatigued T, remaining in this state for a number of days equal to its Constitution modifier (again, minimum one); if it would become fatigued during that time, it is exhausted T instead. Each day after that period, the creature takes 1 point of Wisdom damage. If the total Wisdom damage exceeds its Hit Dice, the creature is affected as if by an insanity spell.”
The Wisdom damage continues to accumulate thereafter until the creature falls unconscious. Obviously, all effects of a lack of sleep (the fatigue, exhaustion, wisdom damage, or insanity effect) cannot be mitigated in any way except by sleep (although long-duration stat boosts can help delay them). Except for the Wisdom damage, all effects of a lack of sleep instantly vanish after a daily rest as described above. The Wisdom damage caused by lack of sleep can only be recovered by sleep, and once the Wisdom damage drops to the number of Hit Dice or less, the insanity effect ends. Of course, you can choose to take full-day rests or the Hibernate feat to recover the Wisdom damage faster.
For example, a 1 HD Commoner with all 10s for its ability scores can go without sleep for one day (like anyone). After that he’s fatigued for the 2nd day. After that he takes one point of Wisdom damage and continues being fatigued for the 3rd day. After that he takes another point of Wisdom damage and thus suffers the insanity effect from the 4th day on. By contrast, a Level 2 Human Fighter with a CONmod of +3 can go three days without being fatigued, another 3 days before taking wisdom damage, and another 2 days before suffering the insanity effect.