A magic portal between our world and another earthlike one opens near a large city of a first-world country in the present day. Governments on both sides learn about it and take control within days.
The aliens on the other planet are at a similar tech level to us (including weaponry!) with relatively similar societies. Their language don't resemble anything close to any human language. The aliens have relatively similar biology (i.e. bipedal, multicellular, DNA based, etc) for reasons that are out of scope of this question.
The portal is about 10 metres in diameter, hovering just above ground level, and will not close but cannot be widened or moved.
Assuming that both humans and aliens are eager to cooperate, how long would it roughly take, at a minimum, to go from the portal opening, to civilian aliens being able to immigrate and live in the nearby human city?
I'm writing a story about one of these immigrating aliens and I want to know roughly how long humans have known about the aliens by the time they're able to move over.