Setting timer on window unit to turn on and off

I found a manual for the Hitachi PC-P1HE which might be similar to your model. According to the manual, if the unit is turning on by itself, it could be due to a malfunctioning remote control or a timer setting. Here are some steps you can try to resolve the issue:

Check if the remote control is malfunctioning by removing its batteries and see if the unit still turns on by itself.
If the unit still turns on, check if there is a timer setting that is causing it to turn on automatically. You can refer to the manual for instructions on how to disable the timer setting.
If none of these steps work, it might be best to contact your service contractor of HITACHI for further assistance

Possible checking the power switch, the timer control unit and also if there is any power trip in the circuit.
The most possible chance could be related to the timer unit, so reset the timer control , try setting to higher levels and see if the power holds on.

what temp are you setting it at? are you certian its the sleep timer shutting it down?

Use the remote to enter the timer to switch off - OFF timer setting and the On timing after setting the clock on the remote
Once this is presetted the unit will continue to work shut of in the thermostat settings and fully cuts off power in the set off time.
later the set will come back in the set on time and work till the thermostat setting is reached.

To shut off the timer function (turns the unit on at a certain time):
Press the timer button (on the system itself) until the little clock icon disappears from the units display. This deactivates the timer.
Alternatively, you can reset the system to factory default (clear all user inputs and setting from memory)by:
Start with the power on
Turn the unit of using the power button.
Turn the unit on while pressing the Stop/Clear button.


Here is a link to a PDF version of the manual free to download:
http://www.retrevo.com/search/v2/jsp/mytrevo/myTrevo.jsp?page=man

Cheers,
Jer

Setting the ON time (Example: AM 10:15).
1. Press the TIMER button on the Unit for more than
two seconds.
The Timer indicator lights up and the hour digit of the
current ON time blinks on the display.
• When the clock is not set, “CLOCK” and “ADJUST”
appear alternately on the display. Set the clock first.
Press the ¢ or 4 button on the Unit to set the
hour you want the Unit to come on.
Pressing the ¢ button moves the time forwards and
pressing the 4 button moves it backwards. Hold
down the button to move the time rapidly.
2. Press the TIMER button.
The minute digits of the ON time blink on the display.
Set the minute you want the Unit to come on, using
the ¢ or 4 button.
2 Setting the OFF time (Example: PM 1:30).
1. Press the TIMER button.
The hour digit of the OFF time blinks on the display.
(The same time as the ON time will be automatically
set.)
Set the hour you want the Unit to be turned off, using
the ¢ or 4 button.
2. Press the TIMER button.
The minute digits of the OFF time blink on the display
Set the minute you want the Unit to be turned off, using
the ¢ and 4 buttons.
3 Selecting the music source.
1. Press the TIMER button.
The “TUNER” or “CD” blinks on the display.
2. Press the ¢ or 4 button to select the music
source you want to listen to.
The display changes as shown below.
TUNERôCDô(back to the beginning)
4 Setting the volume level.
1. Press the TIMER button.
The current volume setting blinks on the display.
2. Press the ¢ or 4 button to select the volume level.
-- :The current volume level will be used.
0 to 50 :When the timer is turned on, the Volume
will be automatically set to the selected
level.
5 Press the TIMER button.
The timer setting is completed and the display returns to
the display before you set the Timer. The Timer indicator
remains lit.
6 Before turning off the System, prepare
the music source selected in step 3.
TUNER: Tune in to the desired station.
CD: Insert a CD. (Playback will start from the first
track at Timer on.)
7 Press the % button to turn off the System.
In standby mode, you can see the Timer indicator ( )
on the display.
• When the timer turns on, the Timer indicator starts
blinking and the prepared source in step 6 will be
played.
To cancel the timer, press the TIMER button. The
Timer indicator ( ) goes out on the display.
To re-activate the cancelled timer, press the TIMER
button to light the Timer indicator ( ).
At this time, you can see the current timer settings. Each
setting appears on the display for two seconds in the order
of ON time, OFF time, music source and volume.
To change the timer setting, repeat the setting procedure
from the beginning.

I doubt a timer would work because it has electronic controls which would require manually setting the A/C when it is powered up.

You can test the concept by setting the A/C where you want it to come on if you had a timer, unplugging the unit for a few minutes, then plugging it back in. If it doesn't start up where you left it before it was unplugged, then a timer will not do the job you want it to do.

If it does come back on where you want it, a good timer to use for that unit would be an Intermatic hot water heater timer.

Press the *power button* once to start the heater on high power, continuous run. If left at this setting, the unit will run continuously on high power (1500 watts, 12.5 amps) and will not shut off until the unit is manually turned off.
Press the *power button* again, to change to low power, continuous run, (900 watts, 7.5 amps) and will not shut off until the unit is manually turned off.

Set temperature:

Press the temp/timer button until the temperature icon blinks. Use the up and down arrows to set the desired temperature.
The temperature icon will stop blinking and the current room temperature will reappear after the desired temperature is set.

The heater will turn off and on to achieve the desired temperature.

Set timer: (auto off)

Press the timer/timer button until the timer icon blinks. The hour display will appear. The auto off icon will also appear.
Use the up and down arrow buttons to set the heater operation time between 1 and 10 hours. This function will activate once the timer icon stops blinking. The heater will automatically turn off whn the times runs out.

Set timer: (auto on)

Press the temp/timer button until the timer icon blinks. The hour display will appear. The auto on icon will also appear.
Use the up and down arrow buttons to set the heater start time between 1 and 10 hours. This function will activate once the timer icon stops blinking.
The heater will automatically turn on when time expires.

Hope this helps!

Try "playing" with the CountdownTimer feature: Setting the CountdownTimer 1. Press TIMER ON/OFF to enter timer setting mode. The red TIMER icon will flash on the display. 2. To select countdown time, use the TRK (SEARCH?TUNE) / buttons to select the correct time. Press and hold to fast forward or fast reverse countdown time. 3. Press TIMER ON/OFF again to activate the timer. The unit will beep twice to indicate countdown has started. The red TIMER icon will remain lit during countdown. 4. Press TIMER ON/OFF to turn timer off at any time or after it has sounded. good luck