I think it is safe to say that railroading was in general a 24/7 kind of business, it certainly was in the places I worked. Day work was preferable to night work simply because most folks prefered "normal" hours, but night work was routine and it didn't take much to decide to do something at night.
While a lot of factors governed when trains were run, one of the considerations was minimizing meets, especially where you didn't have a lot of open telegraph offices to issue new orders if trains got late. I have a vague recollection of seeing something that suggested that when the San Juan was running the normal practice was to run the Alamosa-Durango freights at night.
But during the oil and gas boom in the 1950's I believe trains were run as quickly as cars, engines and crews could be turned and night or day made no difference.
By 1960 traffic was down enough that they had the "luxury" of a routine of morning departures from Alamosa, Durango and Chama. However these "day" runs often extended well into the nightime hours.
JBW