Scroll past the 844 schedule and see the BB schedule here 2019 Union Pacific Steam Schedule
From the above mentioned official schedule:
Saturday's start "The Big Boy will make several brief stops in communities on its way to Ogden.
Saturday, May 4 Cheyenne Depot
Christening 9:30 a.m. MT
Depart Cheyenne 10:00 a.m. MT
Arrive 11:15 a.m. MT Harriman, Wy
Depart 11:30 a.m. MT County Road 102 Crossing
Arrive 12:30 p.m. MT Laramie, WY
Depart 1:15 p.m. MT Laramie Historic Railroad Depot
E. Kearney and S. 1st St. "
I plan to be waiting at E. of Harriman to catch a run by.