Sleep for an hour

Question

I use a Mac mini as a file server and a media server at home. It's now on pretty much 24/7, which is a waste of energy and I'd like to reduce that energy use but not have to do anything for it. So here is the 'logic' I've come up with ....
+"if no network traffic has occurred in the last 3 minutes, go to sleep for an hour unless you can ping the laptop or frontrow is running"+ --- the latter two cases are situations where i'd like to retain access to the mini even if I havent used it in the last few minutes.
If I dont do anything, it will wake up after an hour and then go back to sleep after 3 minutes.
The only unpleasant situation I can think of is that if I come home just after it has gone to sleep. But in the rare cases that I need immediate access to files I'll have to activate it manually.
My problem is:
*How can I make the Mac sleep for X number of minutes and then automatically wake up again, without the use of an external system and Wake-on-LAN.*

Answer 1

The following C program will generate a date/time n seconds from now in the correct date/time format for pmset.
#include <time.h>
#include <stdio.h>
int main (int argc, char *argv[]) {
time_t timetnow;
time_t timetthen;
struct tm tm_t;
char strtime[256];
if (argc != 2) {
printf ("%s:\nUsage: %s numberof_seconds_fromnow\n", argv[0], argv[0]);
return 2;
timetnow = time (NULL);
timetthen = timetnow + atoi (argv[1]);
localtime_r (&timetthen, &tm_t);
strftime (strtime, sizeof (strtime), "%D %T", &tm_t);
printf ("%s\n", strtime);
return 0;
The program can be compiled if XCode is installed, by saving the program as timeplus.c and then compiling using cc timeplus.c -o timeplus
niihau:TEMP marko$ timeplus 3600
05/21/09 21:43:03