It takes as long as the spring only because they weren't looking. They can stretch the oath that far, they can be disinterested in knowing - but now they know, and so there it is. Elwing of Sirion is twenty-three. Half-man, so fully grown. Sirion is a city of refugees. Elves and Men and, since there are Men, children. Elwing herself has infant children.
They debate whether to send messengers. Debating is allowed, even protracted debating. The Oath, these days, is loud in their minds, and louder when they're pushing it like this, but they drag out the debate for a few months. Messengers will probably be shot on sight. The last time Elwing of Sirion received news of the House of Fëanor it would have been the news that her brothers, twins, aged seven, had not survived the sack of Menegroth.
They send messengers anyway. The messengers are shot on sight. They have good armor, Fëanorian armor, and return home injured but not lethally. Maglor's songs no longer stitch them together. War makes you worse at healing. Maglor's songs are more powerful than ever - he can knock back a wave of approaching enemies, he can make a blade's next touch deadly, he can make them faster and more impervious to danger, but he can no longer do healing.
Maedhros, when he thinks about this, thinks that perhaps there needs to be part of you that is not broken for healing spells to draw on. Or perhaps the Enemy is amused to strip that away first. Perhaps the Enemy finds it suited to the theme as the Oath tugs and yanks and twists them into violence against the lands they once defended and the peoples they once sheltered.
They send messengers to Sirion again. The messengers deliver a plea for the Silmaril, an offer of anything at all in exchange. The messengers do not return at all.
The Enemy is many many hundreds of miles from here but at night Maedhros can hear him in his head. Is it so implausible that I really let you go? the Enemy likes saying. You serve me better free than you ever would have willingly.
The Oath allows them to work slowly. They begin planning the sack of the refugee camp even more slowly than the Oath allows, so slowly that its currents are constantly tugging at them. Any slower and the currents would erode all the things they care about which are not the Oath, and it would be a disaster to go to Sirion once they've been stripped of their capacity to care about anything that is not the Silmaril. So they do not hold out forever. But they work as slowly as they can.
"If you ever ever figure out a way to use it to take me prisoner, or a way to help someone else do that, I order you not to do it and to warn me immediately. If you ever figure out a way to communicate it to someone else I order you to stop them from getting it by any means necessary. If someone else has it, stop them from taking me prisoner. If you cannot stop them from taking me prisoner, kill me."
"And what I want doesn't enter into it, so if there is literally anyone available who can kill you and you can't do it yourself I will, of course, unless I'm entirely out from under you, tell some let's say small child to do it if by any means I can gain the ability to order them to do things -"
"So should I assume in the future that this does not count as something that would interest you?"
He buries his face in his hand. He's quiet for a long moment. "No. Your wellbeing interests me; pointing out when orders will have a very high cost to you is important to me, knowing what tradeoffs I am making is important. You shouldn't expect that I am willing to trade some probability of being a fairy prisoner off against any other good except a Silmaril, though."
"I doubt there are going to be other fairies around for the foreseeable future. This doesn't seem to be the mortal world as it was described to me by the mortal I met. It must be some other world. Which means no one's gating to it."
"We discussed the orders. Do any problems come to mind with this order: 'go to Sirion. Do whatever you believe is likeliest to result in you returning with the Silmaril. Do not give orders to anyone for any reason other than protecting yourself and getting the Silmarils, and use orders that are minimally constraining towards that end.'"
"Yes. Temporary but constraining orders are not 'minimally constraining' but they are often faster to say and safer to rely on. If I go through a lot of convolutions to remove all unnecessary constraint, then anyone who can't remember what I said may be stuck trying to remember my wording and unable to do anything else besides try to remember the order until they're released by a new permission. I wouldn't consider it 'protecting myself' to avoid being revassalized if I met someone who seemed likely to be a pleasanter master than you and they offered an opportunity, and they might or might not be able to convince me not to bring you the Silmaril anyway. If people are alarmed when anyone whose name I know acts on my orders they may attack their allies and this phrasing doesn't let me interfere effectively. I could easily consider it protecting myself to give you orders. You didn't specify I had to give you the Silmaril, just return with it, and I'm pretty sure that would give me a lot of leverage you don't want me to have. The order would be better if you put the first sentence last instead, because recency takes precedence, but it's still sloppy and you'd be better off giving me a simple permission to leave the fortress and to order people who I encounter in Sirion for the next day or however long you want to give me and then relying on me not wanting people to be massacred for everything else. I'm good at this crap, I learned from the best."
"That plus an order that if I am in possession of a Silmaril I must bring it to you. It is the best way to achieve your goals if they are as I understand them and no one in Sirion is going to convince me that you won't really massacre them."
"I have no idea how persuadable you are. There are people in Sirion who witnessed the fall of Doriath. There are lots of people who can tell you how oaths work. If you are in possession of a Silmaril, bring it to me. You can leave the fortress for two days and have to return here at that time if you can do so safely. You can give orders to people in Sirion but not orders that extend more than a day after you've left the city."
"I would probably also benefit from more information about the place if you can tell me. And I still don't have the names."
So he pulls out maps, shows her where they are and where Sirion is. "The population is a mix of survivors of the fall of Gondolin, the fall of Nargothrond, and the fall of Doriath. The ruler is Idril, who was the princess of Gondolin. Her true name is Itarillë," He's sending images of faces. "I haven't seen her since she was a child, I'm sure she's changed. Her husband is Tuor. Her son Eárendil is married to Elwing. They have two young children, Elrond and Elros." And so on.
The names click as they go by, when they're the right ones. Promise is quiet and attentive.