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Don't be fooled by the cute picture of Riko and Momoi on the cover, this is not the fanservice special you were hoping for. Kuroko's Basketball: Can We Do That One More Time? (can I never type this again?) is a thorough companion piece to last season's Tip Off episode. Both are normal length additional episodes included with the season one and two home video releases, and both give more background on the Generation of Miracles. Instead of Kise, this time the episode is centered on Aomine which is inherently more interesting. Kise and Kuroko's relationship was never implied to be particularly important in the series, but Aomine and Kuroko's former friendship was referenced frequently although you never got to see much footage of that time. If you were interested, then now's your chance.
On the other hand, an abridged version of these events would show up in a flashback episode in season three, so whichever one you watch first you're inevitably going to be annoyed by seeing some of the same exact scenes twice. Some of these scenes you may have seen even more than that by now (such as the scene where Kuroko puts a popsicle down Aomine's shirt). Though frustrating, there's no way around this unused footage because the original material in this special episode ultimately makes it worth watching. It's a more substantial elaboration on what is by far one of the show's most important character relationships, so it adds more to the general series plot than Tip Off does regardless of reused scenes. However, though it is more detailed and it's nice to actually see what most of the series only talks about, it won't actually give you any significant new facts on the plot or characters you won't get from the series. Just more of an appreciation for them at best. The animation quality and music selection is the same as the series.
With the recommendation to any curious fans out of the way, the question remaining is when the best time is to watch this special. There isn't really a simple answer here. You can do it as soon as you're introduced to Aomine in order to get the most out of future Aomine scenes in it, or you can wait until the flashback arc in season three where this actually fits in the most smoothly chronologically since it's the same stretch of time. You also get to see how the special and series's unique scenes complete each other. In the special episode, Akashi thinks Kuroko may have a special talent, but it immediately cuts to him already using his unique passes rather than the series which goes into how he develops them. Overall, I'd say once you meet Aomine in the series then the earlier you watch this the more you can get from it, but decide what approach sounds better for you.