One of my user always complains about the load on the server, he works in a different location & time zone.

Is it possible to check the CPU activity during specific time/days? let us say for example, i want to check the load on the server at 9 pm to 10 PM on August 22th ? Not the current load. How can i check this ??

You will have to implement a program that does statistics collection, something like "sar" for example, but still depends on the OS. For instance, AIX doesn't have top utility installed by default, it has "topas". vmstat should also be fine, it's present in almost common format on most UNIX-like OSes.

Expounding on what sysgate said, you need to run "sar". One, however, just doesn't "run" sar. Check the crontabs for a line containing "sa1" and/or "sa2". If not, look at the man pages for sa1 and sa2. Once you've been running these for a while, you can look at basically anything in the last month using the "sar" command-line tool.