Why don't you use a Real Time clock?
http://www.ebay.com/itm/DS1302-Real-Time-Clock-Module-with-CR2032-3V-Battery-For-AVR-ARM-PIC-SMD-HE-/141081719032?pt=LH_DefaultDomain_0&hash=item20d92030f8
Look you can take out the IC and build your won connected to the arduino : ) or just use it as it gets to you.
Then you'll have time, date and some bytes of memory for storage : ) and since it runs with a battery, you'll never lose your time setup... cool, no?