I suppose if you REALLY want to know, you can click 'members' under the 'gym logo, go to advanced search, and sort the list by join date...it will give you a rough idea of 'who joined when'...but why does it matter, anyway?
We have a WINNER. Marril is correct. Actually there are several ways to see that information. On many browsers, holding your mouse pointer over the name of a poster (in the left sidebar) will show the following information in the lower left status area of the screen:
The above infornation is what I see when I look at Marril's name. I can also see this same information when I right click on a name and select properties from the menu that comes up. I'm sure there might be a few others, but this should give you a few quick ways to see where you joined in on the long procession of people signing up!