I got my antenna about a week after I ordered it, which is not bad at all. Installation was really easy, but there were a couple issues with my particular install.
Firstly, as others noted, the 5/16" bolt is actually a Phillips head screw, at least on a '95 S. A ratchet definitely is helpful though, so be sure to get one that you can hook a screwdriver bit to. Probably a good idea to tape things together so the bit doesn't fall off inside your Sol! It really is tight in there too, so use your smallest ratchet.
Secondly, I have to say the outside fitment wasn't quite as nice for me as others experienced. The included gasket (that goes between the body and outer top part of the antenna on the outside of the car) was too thick and didn't really seat well for me. I probably could have gotten the new gasket to work with more patience, and may try it again sometime, but it was just not letting me line things up. So I just used the old one, which unfortunately leaves a very small gap. It doesn't affect the protective ability of the gasket, it's just slightly off-looking if you want to be picky about it
I should also mention the stock mounting bracket is far too large to properly clamp down on the new, slimmer antenna; you'd have to stick something else in there to shim it, or otherwise use the included hardware. It doesn't seem to make much difference once the top part of the antenna is in place though, so I'm not worried about it.
One more thing: the paint (I thought this was anodized?) on the antenna is not really on there too good. Just pulling it out and adjusting it for length resulted in a thin ribbon of paint being shaved off by the adjacent telescoping piece. So be careful with it if you want it perfect-looking.