Hitachi RAC-S28H2 Instruction Manual page 15

Explanation of the sleep timer
The device will control the FAN SPEED and room temperature automatically
so as to be quiet and good for people's health.
You can set the sleep timer to turn off after 1, 2, 3 or 7 hours.
NOTE
G
If date or current time is not set, sleep timer can not be set.
G If you set the sleep timer after the off-, on/off- or off/on-timer has been
set, the sleep timer becomes effective instead of the off-, on/off- or off/
on-timer set.
G You can not set other timer during sleep timer operation.
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