I want to give away a prize.

[BellGab.com]

is there a technical/performance reason why one shouldn't set the users online time to 24 hours?  or is it just a matter of standard forum practice?  i always thought it was nice for people to easily see who was online during any given day.

Yes, there are a number of good reasons for not doing it. Though it really depends on how you do it.

Doing it through the Users Online Today mod is safe. Doing it the way you are is wrong.

1. It bloats log-online table. This is queried every single page load. You want to keep it lean.

2. It makes people appear to be online when they are not. Right now it says you have 1430 users online. That's about what's typically online here - and this site has some serious expensive servers to manage it. Only here the window is much smaller.

3. If someone opens a page and then closes their browser, they will continue to be online for all systems purposes for the next 23 hours and a bit, in their profile, in the poster information and so on.

oh, and thanks for outlining this.  i've changed it back to 15 minutes.