Generally it seems to be the beginning of april. Check their website occasionally, the date will be posted there when they have one. Also, make sure you've got a fast internet connection when registration opens. It was what, 35 minutes before they ran out of spots this year?
It's always on a Saturday around ~10AM MST, so as long as you don't work on Saturdays, you're good. Once they announce the date / time just be on your computer hitting refresh 5 minutes before the page goes live. And I'd go ahead and book your hotel room now (anywhere in Ouray is fine), you can always cancel the booking if you don't get in.
Two years ago (the ~37 minutes sell-out year) I registered using my phone in a hotel room in Telluride while getting ready to go skiing. Last year I was on a cruise ship during registration and paid for the internet package all week.
But +1 to @Iconic_ 's note, if you don't get in with the initial group just make sure you get on the wait list. Lots of people from the wait list get in every year.
Still waiting to see if the Summit bosses are going to change up how they do registration this year, last year's ~30 second sell-out was unprecedented.
Either way, good luck! Ouray is an amazing town and this is a well organized event, come for both the trails and the people / vendors. If you're just coming to offroad, there are definitely less crowded times to be there.
Everyone who has ever been to the Summit has probably driven pass this stone garage near Ironton Park and wondered what is is. Well now you know.
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