@Zhengo personally, I love it when there's foreshadowing in the story. So if there's a secret you feel you just can't reveal too soon because it doesn't happen organically, drop hints along the way. Even if your readers won't catch up on them immediately, you can direct them to these little things later and have them go "OOOoooh frick!" – I love these moments when I scroll back in stories (or, traditionally speaking, flip the pages) because I feel like I have seen something before, only to then realize that I could've known all along. Only I couldn't because the final puzzle piece was missing.
I also recently read an advice on Twitter about this problem with secrets, I think it was from a literary agent. They said that you want to advertise the BEST stuff from your novel in order to garner interest; and sometimes, these best things are some little secrets that your characters don't know about quite yet. So if I were to pitch my novel to someone, I'd definitely include my 2nd protagonist's relationship to the antagonist in said pitch, even if it's only revealed in about the middle of the first act of the story.
So think about what you want your readers to know about the story's backdrop that differs from the knowledge the narrative offers your characters along the way. What effect do you want to achieve within your readers? Are they supposed to be just as shocked/surprised/whatever as your characters? Or do you want them to know beforehand, so they can empathize with your characters on their way to the truth? Or do you want to foreshadow rather than spill the beans, in order to string along your readers?
I feel it all comes down to what your goal is, really. As that differs so much from story to story, it's hard to give definitive advice, so maybe these questions give you some more pointers. 
Yeah, that's the problem with serialized content, we kinda need to drop important things more often than in "traditional" novels and comics because it takes a bit longer for things to resolve themselves. Hard to always account for our readers' memory. xD