duration of "online?"

I made a modification some time ago, when my board was young and I wanted it to look busy, which extended the length of time that a user appeared in the "who is online" list at the bottom of the page.

Trying to undo this has proven to be a bit of a pickle.

I see all my code in the index.php and in the online list at functions.php but I don't see where the duration is set anywhere.

Must be somewhere else, but I can't suss it out.

Does anyone know?