Forword: Take heed and bear witness to the truths that lie herein,
for they are the last legacy of the Horadrim.
There are too much information out there about Double Recurring quests, too much to grasp, and many of which lack clarity and certainty for people to rely on.
Rumor says that the clearest, most concise and most reliable instructions come from a player called Bewildered Zeratul, who through personal experience and self-experiment, screened out the chaff -- information that is unimportant -- and kept the critical, as below, the validity of which, still, no one can be 100% sure.
Unfortunately, the clearest, most concise and most reliable version of instructions were later lost, what can be found is the following equally redundant, tediously long draft of that version. He wrote:
"Seekers of the Double Recurring quests can find them not early than the Late Middle Ages.
"To understand this you must first know the very fundamental fact that there are quests slots and there are quests. And the quests are categorized into three types. There are story quests, side quests, bonus quests, and recurring quests. But wait, that is four types of quests! Oui. You noticed. It works the same way as the Nine Pieces of Eight in Caribbean, but how can that be? -- Very simple. The quest slots. There is a slot for the story quests, a slot for the side quests, and a slot for the bonus quests, but there is no specific slot for the recurring quests. It occupies whichever slot that has run out of quests, be it "side", be it "bonus", and people that took the time travel machine and returned from the distant future also told us that you can also run out of story quests, and thereby have all three slots occupied by recuring quests, which means, more than double, but triple RQS. The benefits of the RQS are outside the scope of these instructions but bascially, you can either do something that fulfill the conditions of multiple RQS at the same time, or you can use the reward of one RQ to fullfil the conditions of another; there is no need to elaborate herein.
"SO basically you want to obtain as many of those slots and "run out" of quests in those slots. You do so by either completing all the quests, or sometimes Abort all of them. Questions: -- Are the story quests abortable? No. -- Are the Bonus Quests abortable? No, unless when the quest giver specifically says "you can abort this quest" in which case to abort every time when told so is a better option (**need verification though); and -- Are side quests abortable? Yes ("Most of the time" they say). Some also say if you abort quests, you will miss out some good rewards in the end, taking the Jester (Robin) series of quests with diamonds reward in the end as an example. But Bewildered Zeratul found that in most cases, the difference between completing / aborting the side quests is insignificant, compared to the benefits of having recurring quests available. So there you go, you just abort abort and abort all the side quests to receive Recurring Quest Slot No.1. No let's go on to address the Story Quest slot and Bonus Quest slot.
"The reason we need to talk about the Story Quest is not to acquire a RQ slot from it also, which is only possible by the end of All Eras (Mars, to be specific, at present). The reason we need to pay attention to it, is because of the correlations between/among the different types of quests. The correlationship is this: The bonus quest sequence is triggered by one specific story quest; the side quests are also, sometimes, triggered by specific story quests, or some other times, they are triggered by advancement in the Continental Map and in the Technology Tree, just like the story quests. They story quests are triggered / driven by Map/Tech knods.
"This is the part that no one can be 100% sure because, the construction of each city takes years (of player reality time) and some story quests have multiple versions and the player can only get one version. The choice can affect subsequent other quests, sometimes not immediately, but a few quests later, by the end of a series of quests, which makes it even harder to figure out what leads to what, not to mention most players never read the description of the quests but only click the buttons in a hurry. The story line is actually the most interesting part of the game actually -- spoiler alert your very first Adviser in the game will betray / rebel against you at certain point and be replaced by a 'princess' a.k.a the 'fair maiden'. Remember the words 'fair maiden'; it is one of the two keys that guarantees double RQs.
"The earliest time in game to obtain Double RQs is the LMA because the earliest very first bonus quest slot is presented in LMA, and that is why they are called 'LMA bonus quests' on Fandom. Some complain it is not possible earilier than that because one story quest asks to "Build a Ruin Tower" before the bonus quests can appear. That is not the point. All those bonus quests fit into LMA if you read the narratives. It is just that the Ruin Tower quest makes the LMA signature definite.
"It doesn't matter if you advance too fast / too far in the continental map, as long as you do not complete the corresponding story quest. Leave the story quest conditions fulfilled, but do not grab the reward. Halt it there. In short, one possible way to "screw" the RQ is advancing too fast, in terms of story quests, not in terms of C-map as many believe. However, there is another possibility, another extreme -- yes, it is advancing too slow, in terms of story quests, but to this end, it means too slow compared to technology research. OK all these descriptions are too vague and let's be specific. Specifically, attention should be paid to the Story Quest of 'Research a technology that unlocks a cultural building'. It is a quite early quest. Imagine if you have researched all LMA (or even CA and so on) techs while not having completed that quest. Who knows then, how much later in the tech tree can you find another cultural research to pass that particular quest?
"While being triggered by C-Map and Tech, the story quests (or one story quest) in turn trigger(s) the bonus quest sequence (and some side quests). And that's it. The "Fair Maiden" is the keyword. It is a story quest name, it is also your future 'first hand', adviser/quest giver, a.k.a the princess, who will replace the former adviser who will 'betray you'. Do not advance the main story quests too slow and got stuck at unfinished "research a cultural building" quest without remaining techs to research; and do not advance the main story quests too fast, either, and stop right there, at the "fair maiden" quest. Not too fast, not too slow -- that's the only trick you need to remember to secure the double RQs and make your dream come true. All the other information is noise. Do not stuck early at 'research a cultural tech' and do not go beyond the 'maiden' quest. One is related to techs and the other is only about the click of a button. All the talks about C-map are unimportant.
"Personally, in Bewildered's opinion, the earliest Double RQ is a loophole. The slot for bonus quests is presented, at the start of the mainden quest, but the bonus quests themselves have not yet appeared, waiting for the maiden quest to be completed. Thereby the recurring quests occupy the slot not after all bonus quests but before them. It is also possible to actually complete the maiden quest, and complete all the bonus quests thereby unleashed, and the RQ slot No.2 will return. It can be called 'the hard way' but why take the hard way when there is the easy way, by means of NOT clicking a green, ticked button? It is possble to finsih all bonus quests in LMA (becasue again, Fandom calls them "LMA bonus quests") even though the conditions for some of those quests are 'CA tasks OR LMA tasks'. So, relax, it is an 'OR' in between."