Our total bandwidth estimate for the first three hours of an event with an expected 20,000 people in attendance is now 400Gb per hour.
This will not be the only traffic generated by your guests. Average data usage by US mobile subscribers is currently 100Mb per day. If 80% of that data is spread between the hours of 8am and 10pm that equates to 6Mb per hour per user. Total traffic of another 120Gb per hour.
That brings us to a total of 520Gb of network traffic per hour in the first three hours of the event.
I've been looking around for a good breakdown of numbers surrounding internet traffic at events. This post, penned by event WiFi company Tour Tech, breaks it down step by step.
As well as that, they were so good as to a) bring up the nostalgia that comes with Pokémon Go and b) provide ways to avoid internet overload at events that aren't just "use our services."