So, here's a very ROUGH draft schedule for a train like that...with a made up name...
Western Continental
Amtrak Train #25
Southbound
Dep Seattle 745AM
Arv Portland 1145AM
Dep Portland 12PM
Arv Boise 11PM
Dep Boise 1130PM
Arv Salt Lake City 7AM
Dep Salt Lake City 730AM
Arv Las Vegas 230PM
Dep Las Vegas 300PM
Arv LAX 10PM
Amtrak Train #26
Northbound
Dep LAX 8AM
Arv Las Vegas 3PM
Dep Las Vegas 330PM
Arv Salt Lake City 1030PM
Dep Salt Lake City 11PM
Arv Boise 630AM
Dep Boise 7AM
Arv Portland 6PM
Dep Portland 630PM
Arv Seattle 1030PM
Since this is all hypothetical, why not throw out all the 'rules' and do something like this. Overnight between LA and Las Vegas. This serves Cedar City(Milford) the gateway to Zion and other parks during afternoon hours. It also gets into Pocatello and Shoshone during morning or evening hours to connect with Yellowstone and Sun Valley. And.........if you use the Green River cutoff on the UP from Pocatello, you can combine the Pioneer section with the CZ westbound and have your own late departure from Denver eastbound. It's interesting. Northbound the two trains combine in Pocatello and southbound they split there.
PIONEER
Pioneer Pioneer
8:00 AM lv VANCOUVER BC arr 10:00 PM
2:20 PM lv SEATTLE arr 3:55 PM
5:50 PM arr PORTLAND lv 12:15 PM
6:20 PM lv PORTLAND(PT) arr 11:35 AM
5:55 AM arr BOISE lv 1:15 AM
6:00 AM lv BOISE arr 1:05 AM
8:15 AM arr SHOSHONE(MT) lv 11:00 PM
5:30 AM lv SUN VALLEY arr 1:30 AM
7:30 AM arr SHOSHONE lv 11:30 PM
8:20 AM lv SHOSHONE arr 10:55 PM
10:00 AM arr POCATELLO lv 9:15 PM
6:45 AM lv WEST YELLOWSTONE arr 12:30 AM
9:45 AM arr POCATELLO lv 9:30 PM
10:30 AM lv POCATELLO arr 8:00 PM
2:50 PM arr GREEN RIVER lv 3:40 PM
2:55 PM lv GREEN RIVER arr 3:35 PM
8:25 PM arr CHEYENNE(BOWIE) lv 10:05 AM
8:30 PM lv CHEYENNE(BOWIE) arr 10:00 AM
10:30 PM arr DENVER lv 8:15 AM
11:10 PM lv DENVER(MT) arr 7:15 AM
7:41 AM arr LINCOLN lv 12:14 AM
7:47 AM lv LINCOLN arr 12:08 AM
8:59 AM arr OMAHA lv 10:39 PM
9:14 AM lv OMAHA arr 10:29 PM
6:50 PM arr CHICAGO(CT) lv 2:00 PM
Desert Desert
Wind DESERT WIND Wind
11:15 AM lv POCATELLO arr 9:00 PM
1:45 PM arr OGDEN lv 6:15 PM
1:55 PM lv OGDEN arr 6:05 PM
2:50 PM arr SALT LAKE CITY lv 4:45 PM
3:00 PM lv SALT LAKE CITY arr 4:35 PM
3:40 PM lv MILFORD(CEDAR CITY)(MT) lv 1:05 PM
10:45 PM arr LAS VEGAS(PT) lv 7:00 AM
11:15 PM lv LAS VEGAS arr 6:30 AM
7:00 AM arr LOS ANGELES lv 11:00 PM