BZN's last arrival was at 9:56 PM (MDT).
MSO's last arrival was at 5:18 PM (MDT) (later flights were canceled).
GEG's last arrival was at 12:45 AM (MDT).
DL2639 arrived in GEG at 1:15 AM (MDT).
BZN and MSO were probably closed for the night when 2639 started to divert.