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From their website:
Extra Life begins whenever you want it to! Just find a date and time that works with your schedule and start playing! If you can make it, our National Game Day will begin at exactly 8 a.m central time on Saturday, October 25th, and ends at 8 a.m on Sunday, October 26th. Remember, if you can’t make this day work, you can do Extra Life whenever it's convenient for you. Some folks even break it into two segments.