I assume that you are looking for a way to record when anyone logs into a router. The way that I have done this and had success was to configure aaa on the router talking to an ACS server. I configure aaa accounting on the router and the router sends a message to the ACS server every time anyone logs in on the router (and another message when they log out - so we know how long they were there).
This works. It does not involve any complicated action on the router, does not involve export, and does not have any question of clearing logs on the router.
HTH
Rick
HTH
Rick