We always recommend that you set your Sleep Time alarm right before you actually go to bed each night for maximum accuracy since it begins tracking your sleep patterns as soon as you start the alarm.
For iOS:
Although it is normally not possible to set an alarm more than 12 hours in advance with ST, you can set an alarm up to 24 hours in advance if you go into the Date & Time settings for your device and enable "24-Hour Time" mode.
For Android:
Unfortunately, you may only set an alarm for up to 12 hours in advance on the android version of Sleep Time.
For iOS:
Although it is normally not possible to set an alarm more than 12 hours in advance with ST, you can set an alarm up to 24 hours in advance if you go into the Date & Time settings for your device and enable "24-Hour Time" mode.
For Android:
Unfortunately, you may only set an alarm for up to 12 hours in advance on the android version of Sleep Time.