That is my point in relation to the Serum, nothing points out to what the Serum does, it doesn't even remotely tell you if it reacts as a evolution trigger or a instant lvl5 Serum, thats why i say that we will only know futher down the line, one thing is having small hints and small factual evidence to prove it, but at the moment saying what it is or is not is supposition at most.
Let's go over this once again...
During the fight with Ella(lvl 4), Clark(lvl 4) and Lexi(lvl 4) struggled. They decided to take the serum to evolve mid fight. This is something which Ella acknowledged.
Afterwards, they're ordered by Xanthe to watch the Minyak. After Clark kills it they report back to him. It is there that it's confirmed, by Clark, that after they took the serum, their strength is "way beyond any superhuman recorded" and they can now match S Class Monsters. They reached lvl 5 via the serum and he also states that "once the rest of his team(Nico and Deus) and Cthulu receive it as well they will be able to stop the monsters". We know what the Serum does from here. No speculation needed.
Way later, after the MC beats Klaus, Xanthe tells Nico to retrieve their corpses. Nico literally tells him she wants the serum as payment, the same serum he gave to Clark and Alexis. Xanthe tells her he was going to give it to the rest of her team anyway(which mean't Deus and Her) after Zaman and Cthulu. He agrees to give it her after her job is done. She's happy and goes to get the corpses.
Lets Jump even further to Ella's and Jake Hero infiltration and you see that Clark states that "from our last encounter, you should realize we're in different leagues now. We've reached our final evolution" to Ella. So there you go, they reached lvl 5 during that first fight. The icing on the cake is his statement afterwards. "As of last night, there are twelve among us that have reached lvl 5" indicating that Nico indeed took the serum.
You might say "Well, he could be talking about Zaman and Cthulu. We don't know how many were lvl 5s were there and that doesn't mean Nico". I would then just say that Nico showed desire for the serum and Xanthe said he would give it to her after her job so it points in favor of Nico taking it after she received it. She has no reason not to and wouldn't hold onto it after asking for it in the first place.
There should be no more confusion on this. Hopefully this clears everything up. If it still doesn't, then that's fine as well and I don't plan on trying to pursue this topic any further as it's already blatant in the game. Also a small detail, the serum Ella stole to reach lvl 5 was the exact same color as the one those 2 took and it instantly gave her evolution. There's no delayed reaction, it's instant so you have the 3 people who used it on screen all evolve to lvl 5 after taking it.