I've joined both the Railroad and found the Institute. I've decided upon the Railroad for this playthrough. My question is, how long can I keep playing both sides before I am forced into a choice of one, please?

Also, does the Railroad and/or Institute have continuing radiant quests after you finish the main quest, please?

This is my first playthrough so please go easy on the spoilers.

SPOILER BELOW...although, it's been ~6 months since the game came out, so at this point, most reasonable fandoms would have proclaimed the spoiler period well over by now...

In any case, the Battle for Bunker Hill seems to be the draw point for Institute vs. Brotherhood vs. Railroad. You have to pick a side here if you're rooting for one of those three factions (the Minutemen don't have a stake in this battle, so it doesn't matter to them about the outcome). You don't have to fight in the battle, per se (I didn't...I sat back and watched it unfold), but you still have to decide what to do with the synths in the basemant once the above-ground & below-ground battles end. If you let the synths go or port away without a decision, you anger Father and the Brotherhood once you go back to either side. If you kill the synths, you anger the Railroad if you go back to them.

This quest the part of the game I was most dreading, personally, as I wanted to find a peaceful solution for all sides, but the game designers don't let you do that. Someone has to go if you make it to this quest and accept it.

Personally, I'm hoping for a future DLC that changes the program just enough that a negotiated peace might be an option for the four factions. After all, what's the point of a high Charisma if you can't use it to get people to listen to reason and change their minds???

No I know all that. What I'm asking is what specific mission? I haven't done Synth Retention yet, although i've been handed it after meeting Father. I've also completed all the missions for that Doc fella in the Railroad and I'm now pointedly avoiding Desdemona like a dose of the clap because I know she wants to talk to me about the institute. So if someone can give me the mission where I have to decide, that'd be great.

So I'm good up to that point? I can still do radiants for the Institute?

I just told you what the deciding quest is for the Institute: it's the Battle of Bunker Hill. Once you hit that, there's no turning back. In order to get there, you have to do & complete Synth Retention. As long as you bring back Gabriel (use his recall code) or kill him, the Institute will be happy with you (if you take his bribe or kill X6-88, you lose the Institute's backing and get banished by them). If you use his recall code or kill him, as soon as you turn Synth Retention into Father, he sends you out on The Battle of Bunker Hill quest. Then, you have to choose who to back.

For the Railroad, you can finish up to Operation Ticonderoga. That's where you have to decide for the Institute or the Railroad, because there are Institute synths inside you either kill or turn to their side and betray the Railroad.

I didn't read past "Spoilers below". Sorry mate, but I did make it clear this is my first playthrough and not looking to ruin my enjoyment. All I need is your indulgence with a straight up answer without the spoilers - the mission name, please. Thanks.

Thank you both.