I previously rode this route on a regular basis before the schedule was changed. Even if the Sunset Limited is late most stops will last at least a few minutes. The shortest stops are nearly impossible to use for photographs. The staff will generally only open one or two doors and even if you happen to be near that door it's likely to be a one way trip for that stop. Some stops will last several minutes and be mentioned as "smoke breaks" to the passengers. These stops will generally be long enough for photos near the tracks or around the station area. Not all smoke breaks are strictly scheduled so you might end up losing some and gaining others depending on the circumstances. A few stops will last long enough to get off the train and go exploring beyond the immediate area. Just make sure you know exactly what time it is and precisely when the train will be leaving. In my experience the Amtrak website is the best resource for determining the true departure time. Printed timetables are sometimes outdated while the onboard staff will sometimes claim the train is going to leave well before the actual departure time. Nobody is going to stop you from leaving the immediate area but if you're not on the platform when they blow the horn and the conductor calls "All Aboard!" they will absolutely leave you behind.
