system
Given the following post, respond as if you're commenting on Reddit:
human
[Stargate] How long would it take to evacuate the Earth through the gate?

My first blush estimate: 7 billion people at 1 person/second gives 7 billion seconds or about 222 years. Not sure how you'd maintain that rate, though. Supplies would have to be sent, too, and there's the 38-minute window to worry about. And not every threat is going to wait for two centuries while you evacuate...
gpt
Trains, that's how. The new maglev being developed to replace the japanese bullet train can hold 1000 passengers and can travel at 310 MPH. The train is about 400 metres long or about .25 miles. That means that one of these trains could cross the event horizon in 3 seconds.

So 333 people per second. (if you have an infinite supply of trains travelling non-stop.

So assuming you have a massive rail network with enough loops to keep these trains at approximately full speed, so you can put them into a holding pattern while the gate spins up and down, lets give a 5 minute safety margin during dial up (don't need one later as gates won't shut down while an object is in transit) let's be generous and say 20 seconds between trains. That's 86 trains through. 

By the time the gate has shut down, the first train will have unloaded and be on it's way back. Because these trains are empty, they can go faster and we're also comfortable with cutting the safety margins, so say 12 seconds per train, means all 86 trains can be back in 17 minutes 12 seconds (round it off to 20 to give a safety margin in there) When they return, you've got another 86 trains ready and waiting to go.

Add a minute for each dial up sequence and you're looking at precisely 1 hour for 86,000 people or 23.8 people per second.

With the current world population of 7.4 billion, they'll be through in 9 years, 8 months and 6 days.

You would need 2752 train carriages though. You could also cut the safety margins required by stringing more carriages together but you would need more time to unload and more carriages may slow things down too much.