#include <time.h>
char*w = "AAAA########+++///9999AA Good %s!\n\0Morning\0Day\0Afternoon\0Evening\0Night";
int main(){time_t t=time(0);return printf(w+25, w+w[localtime(&t)->tm_hour]);}

//bisqwit's code

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>
#include <sys/time.h>

void setDate(const char* dataStr) // format like MMDDYY
{
char buf[3] = {0};

strncpy(buf, dataStr + 0, 2);
unsigned short month = atoi(buf);

strncpy(buf, dataStr + 2, 2);
unsigned short day = atoi(buf);

strncpy(buf, dataStr + 4, 2);
unsigned short year = atoi(buf);

time_t mytime = time(0);
struct tm* tm_ptr = localtime(&mytime);

if (tm_ptr)
{
tm_ptr->tm_mon = month - 1;
tm_ptr->tm_mday = day;
tm_ptr->tm_year = year + (2000 - 1900);

const struct timeval tv = {mktime(tm_ptr), 0};
settimeofday(&tv, 0);
}
}

int main(int argc, char** argv)
{
if (argc < 1)
{
printf("enter a date using the format MMDDYY\n");
return 1;
}

setDate(argv[1]);

return 0;
}

The world will end when time_t overflows...