the Land of Dragons and the sword of hephaestus

[GorN]

hi, i've got 1 doubt

I went to sheterra when my level wasn't high enough but i've collected some quests, among them the hephaestus quest in which you have to kill 15 dragons with his sword. In this quest, the game give you the chance to go to the world of dragons visiting another character on sheterra (something similar happened on KBTL). However, as my level wasn't enough to go to that place, i leave the island with the sword.

Now, i've almost killed the dragons needed to complete that quest and i'm afraid that, if i do so, i will be unable to go to the land of dragons. is that correct? Must i open the portal before i kill the 15 dragons with the sword? i don't want to miss the chance of going to ulrax!!