It's another question !
For Windows, the more simpler is to run systray application (when you install you have ability to run systray when computer start) : with systray it's easy to start agent (even you are not local administrator). Else the agent is a service, so it could run more than once a day ... else you can launch 'ocsinventory-agent' (with '/force').
For Linux, see crontab or simply run 'ocsinventory-agent' (I suggest set a logfile and use --debug)