Numbers over TC names on mainpage

[mongoose1983]

I'm curious. I just ran through the mouse pointer on my laptop's screen over some names of TCers online on the mainpage and there's different numbers appearing. What do these numbers mean??

[TWINSET]

In the 'online' section, bottom right?

Pretty sure it's some sort of time online indicator

Not sure what the unit of measure is though, I just logged on and I'm up to '4' already