The portal first needs to be (1) activated and (2) then can be used to bring Nyx over if you paid your debt to the guild.
step (1) you do at 18:00 with the activation code gem combo written on the room walls near to the console (B+P+G)
step (2) you do at 19:00 with G+P+G (look int the Nyx quest log entry, not 100% sure about colors off my head)
after (1) also the training room becomes available