In any period of time: Earth wouldn't even notice. Magic doesn't exist. The portal would never form on our end, and even if it did on theirs, they'd be fucked like a Stargate that had its iris closed. Just splat-splat-splat-splat-splat as they arrive to nothingness.
Even if it did form, they'd have no magic when they arrived. Since there's no reason to believe Warcraft is set in the past, that'd also mean they'd be arriving right now, which also means that after the initial arrival and the local militaries were alerted to what was going on and could respond, the majority of the orcs would be fucking obliterated through simple air strikes, since they'd have nothing that could counter that. What was left would be "collected" and experience some truly horrific shit under medical investigations just as if they were aliens--because they are. And with zero legal protections, any country on the planet could pretty much do whatever they wanted to them without any repercussions.