Interesting: in this article, EFF praises Reddit for its quick publication: "Published within 30 days of the reporting period.... That means more recent, and potentially more relevant data." But in the FAQ about warrant canaries, also published by EFF (and linked from this article), they recommend otherwise: "How often should an ISP publish the warrant canary?
Various ISPs have published canaries on a wide range of schedules. To allow time to file a case and for the court to rule on the important legal questions, we suggest at least few months between the transparency report and the time period covered."
So it's not really clear what the best practice is here.
Reddit has never had a warrant canary, so the recommendations on that page have little bearing on this. Even if reddit did get a couple of NSLs, it gets so many actual requests for information that it grants that there's little reason to have one, especially given that it could report it received 0-249 of them 6 months later anyways.
So it's not really clear what the best practice is here.