Nearly a year now. As for why and how, a Biblical Seal brought most of us here. Lucifer is trying to take over the world. There's no way home unless the Seal decides to send us.
No worries Jane. But as you can see, quite a few of us are here. Myself, Darcy, Thor, Tony Stark, my wife Natasha Romanoff, Loki...and those are just from our immediate version of Earth.