When does 24hr check in get DST?

I'm on a redeye flight tomorrow, and my Kayak and TripIt alerts reminded me of the flight departing in 24 hours. While it is true that my flight leaves in 24 hours, UA doesn't think so (yet). Obviously the system operates using current local time (my flight departs close to midnight mountain time, not 11pm) because I'm not allowed to check in yet. Does anyone know when the UA check in system switches over to daylight savings time?

Thanks!