to continue.. if u watched the play the cave gave origin to time travel. Meaning that some how and some what vecna is using the cave to go back in time or use the kids to travel in time to resolve something. But also when erica is in class talking about the wormhole, why was that the only scene talkingnabout wormhole and time distortion, i think they included that to talk about the relm inside the wall where he is collecting the kids to use their powers supplied by the mind flayer to go back in

Definition of "five (number)" from the Oxford Advanced Learner's Dictionary.