Comorbid insomnia has also been reported to reduce CPAP adherence [3]. Therefore, managing insomnia is important. Cognitive-behavioral therapy for insomnia (CBT-I) is a good treatment option for insomnia even in patients with OSA [4]. While treating insomnia using CBT-I, it is important to ask the patients about their sleeping schedule (from what time to what time they want to sleep) [5]. It is generally accepted to sleep for approximately 7–8 hours [6]. Insomnia patients tend to go to bed earlier than they should since they believe that early bedtime may lead to early sleep onset time. However, based on a two-process model [7], which proposes that linking circadian regulation and homeostatic drive is needed for good sleep, enough duration of wakefulness is needed for short sleep onset latency. This means that early bedtime does not guarantee short sleep onset latency [8], since homeostatic drive was not activated for the short duration of wakefulness. Notably, older people tend to go to bed earlier in the evening [9], which could be attributed to insomnia, as a form of advanced sleep phase syndrome in certain cases. Therefore, delaying bedtime could help reduce sleep onset latency.

Lack of daytime activities may also aggravate insomnia symptoms. Sleep-deprived patients tend to spend their daytime lying down on their beds to compensate for the lack of sleep during the previous night. We cannot appropriately manage insomnia symptoms if we do not assess patients’ daytime activities. For 7 hours of good sleep, 17 hours of activities are needed [8]. This suggests that 17 hours of activities are needed before wearing a CPAP mask to reduce the possibility of nonadherence, which comes from sleep disturbance or low sleep efficiency.

To improve CPAP adherence, deciding and specifying the ideal time to wear the CPAP mask is essential. Otherwise, the patients will start CPAP whenever they want. Let’s say a patient with OSA wears CPAP masks at 9 _PM in order to get to sleep by that time. If he regularly wakes up at 4 _AM, we can imagine that he can easily fall asleep at 9 _PM and this regular sleep-wake cycle (approximately 7 hours of sleep) may reduce CPAP nonadherence. However, if he wakes up at 7–8 _AM, the longer time in bed might reduce his sleep efficiency, and consequently reduce CPAP adherence. In this case, to make it easier for him to fall asleep, we should teach him to delay his bedtime until approximately midnight. At the same time, we should align the time of starting CPAP use with the bedtime.

It is well accepted that 4 hours of CPAP use is ideal, since it may reduce daytime sleepiness [10]. From what time to what time do you instruct patients to wear their CPAP masks for at least four hours? From 9 _PM to 1 _AM? From 2 _AM to 6 _AM? To enhance adherence to CPAP, physicians should instruct their patients to align the time they wear CPAP masks with their sleep schedule. For instance, if a patient wants to get up at 6 _AM, we need to instruct him to go to bed at 11 _PM and wear the mask at 11 _PM. When you do not specify when your patient should begin using the CPAP mask, he or she may wear it and go to bed earlier than you had anticipated. This might reduce CPAP adherence, and physicians may not identify the reason. In addition, I propose including the time of wearing the CPAP mask (and duration from CPAP-wearing time to getting-out of bedtime) as a factor that can predict adherence to CPAP.