Not an important question as FT topics go, but I'm curious....

I have a DEN-BOS flight on Sunday that leaves at 6:25p.m. MDT. I checked about 30 minutes ago and noticed that the U/G "pending" had changed to "confirmed", with an F seat assigned.

However, as I draft this, it's still 100 hours and 20 minutes before departure, as it's now about 2:05 p.m. MDT. Does UA go by CDT, without a conversion? Or does the U/G window date back to the departure time of the first of my two flights - 4:33 p.m. from SLC? Or is something else going on here?