HP-UX

           time_t   st_atime;     /* Time of last access */
           time_t   st_mtime;     /* Last modification time */
           time_t   st_ctime;     /* Last file status change time */
                                  /* Measured in secs since */
                                  /* 00:00:00 GMT, Jan 1, 1970 */

ls -l | awk '!/^d/ && /2010-10-01/{s+=$5}END{print s}'

$ cat mysrc/mystat.c

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>

static void psf( char * buf )
{
        struct stat s ;

        if ( 0 > stat( buf, &s ) )
        {
                perror( buf );
                return ; ;
        }

        if ( 0 > printf( "%u\t%s\n", s.st_mtime, buf ) )
        {
                if ( !ferror( stdout ) )
                        exit( 0 );
                perror( "stdout" );
                exit( 1 );
        }
}

int main( int argc, char **argv )
{
        char buf[PATH_MAX + 2];
        char *cp ;
        int i ;
        int clf = 0 ;

        for ( i = 1 ; i < argc ; i++ )
        {
                clf ++ ;
                psf( argv[i] );
        }

        if ( !clf ) while ( fgets( buf, sizeof buf, stdin ) )
        {
                if ( !( cp = strchr( buf, '\n' ) ) )
                {
                        fprintf( stderr, "File path too long: '%s'\n", buf );
                        continue ;
                }

                *cp = NULL ;
                psf( buf );
        }

        if ( !ferror( stdin ) )
                exit( 0 );

        perror( "stdin" );
        exit( 1 );
}