UBB.threads PHP Forum Software Community Forums UBB.threads 6 Version 6 Support many users in "Checking who's online"

I notice that I have many user who just let their browser on the "Checking who's online" page.
I wonder how much it would load my server and if there is any way I can limit the query there, like with "Search" feature when you can search only after xx seconds.

I'm using 6.5.1.1

Thank you for any help on that.