The posts in the series have no post titles using the corresponding field provided by the forum software. However, each post in the series begins with a centered, large-sized caption containing a number (starting from 1), a colon and a keyword that is related to events and plot elements of the One True Comic, such as 1: Beach. Next comes a greyscale (black and white) photograph 553 pixels wide and 395 pixels high, i. e. exactly matching the size of the One True Comic's frames. This is followed by a spoiler containing a poem (with title and author attribution) which is in its turn somehow topical to the noun in the caption, although not necessarily directly to the One True Comic. Finally there is the image that has been shown previously shown as a post attachment (cf. Redundant Spoilers) and in some cases a comment that in one way or another responds to current goings-on in the thread.
The first post in the series was posted at 5:00 am UTC on 24 February 2018 (heretical), i.e. 1 Advent, 4 A.T., and therefore in the run-up to the fifth timiversary. Subsequent posts were timed at one post per day, almost always at 5:00 am UTC as well, which suggests the usage of a bot.
Starting from number 17 in the series, on 12 March (17 Advent), the posts in the series were posted at 4:00 am UTC. This change coincides with the beginning of daylight saving time in most of the USA and Canada. In particular, the usual posting time has consistently been at midnight in the US/Canadian Eastern Time Zone.
The first post in the series was - presumably by mistake - originally already posted on 23 February 2018 (28 Community, 4 A.T.) and subsequently deleted again. However, it had already been noticed by other OTTers who during the following hours reconstructed and re-posted the post, albeit with a smaller version of the original image. This was rendered mostly moot when The Advent re-posted their version of the post, including full-sized image, one day later.
The identity of the author of the posts is currently (as of NP 2638) unknown. The user account of The Advent was only registered on 22 February 2018 (27 Community, 4 A.T.), on which day the user also posted five comments on various threads. Since then, they have only posted the subsequently deleted post on 23 February (28 Community) and after that the posts of the ongoing series, but nothing else. It has been speculated that the five posts of the first day were only made because the first five posts of each account on the xkcd forums are moderated, so that the posts of the actual series which seem to have been the actual point of creating the account would from the beginning not be subject to a moderation-related delayed appearance in the thread.
It seems plausible that the author of the posts is an experienced OTTer who has previously appeared on the One True Thread with another username, but it is unknown whether this is really true, and if so, what earlier username the author had or has been using.
The time of the posts being generally consistent with midnight in the US/Canadian Eastern Time Zone, including the changeover to daylight saving time, may be a rough indication of The Advent's location. However, that is also the location of the One True Author's residence, and it seems possible that the bot was for that reason set up to post using that particular time zone while The Advent is actually based elsewhere.
The poems in the posts are attributed to various authors and therefore seem not to be original content. According to a statement by The Advent on NP2636, the photographic images are also based on works by others, but modified by The Advent.