Set an arduino software clock
There is a Time library which you can import.

Here are things that I found on the Arduino website.

hour();            // The hour now  (0-23)
minute();          // The minute now (0-59)
second();          // The second now (0-59)
day();             // The day now (1-31)
weekday();         // Day of the week, Sunday is day 1
month();           // The month now (1-12)
year();            // The full four digit year: (2009,
                //  2010 etc)
setTime(t);              // Set the system time to the
                      //  give time t
setTime(hr,min,sec,day,month,yr); // Another way to set
                               //  the time
adjustTime(adjustment); // Adjust system time by adding
                     //  the adjustment value

timeStatus();   // Indicates if time has been set and
             //  recently synchronized
             //  returns one of the following
             //  enumerations:
* timeNotSet    // The time has never been set,
             //  the clock started at Jan 1 1970
* timeNeedsSync // The time had been set but a sync
             //  attempt did not succeed
* timeSet       // The time is set and is synced
             //  Time and Date values are not valid if
             //  the status is timeNotSet. Otherwise 
             //  values can be used but the returned
             //  time may have drifted if the status is
             //  timeNeedsSync.     

setSyncProvider(getTimeFunction);// Set the external time
                              //  provider
setSyncInterval(interval);    // Set the number of
                           //  seconds between re-sync


And obviously,

#include&lt;Time.h&gt;


Tell me in the comments if you need more help.