maybe he was being trained up by Bach, learning secret Quincy Techniques that will let him fight on par with Ichigo, or possibly he was being tested by Bach to make sure he's the real deal. Or maybe Kubo just wanted to crank up the drama a bit by waiting
the theory was that there were 26 Stern Ritter, in the same way there were 10 Espada, of course now that 5/6 of them have been pwnd they're be down a few, in fact I think that's probably why they introduced the new ones now, the next big push is coming and they needed to bring in some bad guys to replace the ones that got killed in the previous invasion.
p.s. Kaj the random footsoldiers are called "Soldat", they're the basic Quincy troopers, and I think the gunfighter guy that took Shunsui's eye is the general of them, or at least he was in charge of them for that attack.
EDIT:
Hmm, I just had a thought... Wouldn't it make more sense for the Arrancar that was pointing their blade at Urahara to be Neliel, back in her adult form? We know she was with Orihime and Chad while Ichigo was fighting Opie. Shortly after a "mysterious stranger" cuts Opie in half and we only see their blade. At a later point, we see Urahara, Chad, Orihime and hear a mysterious other person...
Am I the only one that thinks it's Nel?