Hitachi RAD-18NH7 Instruction Manual page 13

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.
NOTE
G If you set the sleep timer after the off or on-timer has been
set, the sleep timer becomes effective instead of the off or
on-timer set earlier.
G You can not set other timer during sleep timer operation.
G After sleep timer time is up and when press sleep button
again, the sleep timer will be set as last setting.
G Sleep timer effective only once.
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