Clock Problem - Looses an hour, but does not happen all the time.

This is not the Asus Z87 BIOS freeze clock problem. When first turned on the clock is not frozen to the time it was when the PC was shut off. When I first turn on my PC the clock is correct and once the clock looses an hour the clock still keeps the correct time, it is just the correct time minus one hour.

I have an Asus Sabertooth Z87 motherboard with an overclocked 4770K. My OS is Win7 Ult 64 bit.

My PC was 13 months old before the first time this happened, then it went five months before the next time, that was in August. Next time was two months later in October. Since the first part of November it has done it in a week, then 10 days and then it went 17 days before it did it again.

To restate the problem, when I first turn on my PC the clock is correct and after an hour or so it looses one hour. Once the clock looses an hour the clock still keeps the correct time, it is just the correct time minus one hour. If I leave the PC on the clock keeps loosing an hour at a time so right now the PC has been on since 3:13 PM, the time is now 6:20 PM, but the PC clock says the time is 4:20 PM. It has lost one hour twice this afternoon since I turned the PC on. The PC will keep loosing an hour at a time if I leave the PC on. If I reset the time and leave the PC on within an hour it happens again.

Once it starts loosing time the only way to get the PC to keep the correct time is to set the clock to the correct time and immediately shut the PC down. When I turn the PC back on it will keep the correct time for anywhere from a week or more. The longest that it has went since the first of November was 17 days before it started loosing time again.

Does anyone have any idea what could be causing my clock in Win7 to reset and loose an hour?