There are Thursday, Friday, and Saturday runs.
If you get caught going against the grain (going West) during one of the runs you will be stuck basically all day. You might be able to get a little bit of movement in between groups, but It's basically a train of about 100 rigs or something that arrive at WH1 around 10AM or so and usually doesn't clear Committee Crossing until like 3 PM or so.
If you're going to try to slip in, do your moving real early and plan to get stuck, or go well into the afternoon.