45 minutes was plenty for this dryer.
If it is like the vintage Kenmore dryers I have used from this vintage, it will dry just about anything in 45 minutes.
It get's really, really hot, then pulls back on the heat when it reaches it first high temp. (I guess that is what they called Soft Heat)
I actually have a Kenmore 70's series that does the same thing. It is from the early 80's, gas version. I was worried that something was wrong with it, because it would get so darn hot. I was always scared that it was going to ruin something. But, it dries everything super fast, and never has had an issue with any fabric damage.
What I really like about this dryer in Gas, is that the burner did not cycle on and off. It just cut back. Kind of like when you cook on a gas stove, and turn the burner down. The gas inlet had a pin that would move into the gas outlet to the burner as the temp got hotter, therefore cutting back on the gas flow, turning down the actual flame of the burner.
I think that then new GE Harmony Gas dryer cuts back like this. I am sure that they don't use the same type of system however. The actual gas silenoid system in the vintage Whirlpool and Kenmore's were made by White Rogers. This type of drying, makes the dryer very fast. No time wasted with cool down, and heat up period of the manifold. Just wish they would go back to this type of gas system, especially with the filter and suction in the front of the drum.
Brent