A two-part minisode story, which holds the impresssive distinction of being easier to place within River's timeline than the Doctor's, especially without having seen the next series.
However its inclusion within the DVD box set of season 32 implies that it's supposed to happen sometime during this set of episodes.
Amy and Rory are referred not only as asleep, but also as River's parents, further narrowing the window down to after Let's Kill Hitler, but before their departure three weeks later in The God Complex.
I think I'd go for placing this straight after the Doctor has left River the diary in Let's Kill Hitler. At the start of this he briefs her on how to use it, which from his perspective seems to be a part of the same plan.
The tension against all of this is that in episode two the Doctor meets his future self. Given the high number of duplicates that the Doctor routinely encounters, it's a surprise that he accepts his future self at face-value, but the real problem is how much this encounter disables the inevitability of his upcoming murder at the end of the series.
On the one hand it would make sense for him to take River to the singing towers of Darillium before his impending death, given how essential the trip is to his saving her in Forest Of The Dead. On the other, I can't help expecting that the bulk of this date will still go and show up in a future full-length episode, which would grant him foreknowledge of his murder's failure.
Mind you, despite this story's brevity, it also squeezes in the start of River's sentence, the launch of her diary-keeping, and her apparently getting used to her new name after Let's Kill Hitler. These are also events that I've been hoping to witness in the series proper, and it's a bit rich to expect me to either shell out a load of additional cash for a DVD box set to see them, or miss out. I've already paid my BBC licence fee, thank you, and not for an incomplete service. The joy of River's character (and arguably the Doctor's) lies in what a jigsaw puzzle her life is, so to withhold some of the pieces sabotages that.
These minisodes are impeccably made though, and trounce the productivity of every other science-fiction series that I've ever heard of, but if licence-payers are expected to pay extra for them, then they should actually be extra to the story, not essential.
Finally, the moment the Doctor realises that River is only pretending to be unconscious to get him to give her mouth-to-mouth, he appears to break the fourth wall with an Oliver Hardy style camera look.
By the way, just a quick reminder, River arguably didn't die at the library, although I agree that all her subsequent appearances would be better if she had.