That could vary with belt speed, type of shirt, color of shirt, and often, what ink. Though someone here with the same dryer could probably give you some starting points, so could could the fine folks at Workhorse. Have you spoken to them? They should be able to answer a lot of your Workhorse brand equipment questions.
Also, the bottom line is the temperature of the entire ink layer.
For that, the gold standard of thermometers is the Atkins Donut Probe which actually buries fine probe wires into the ink layer of a test shirt.
Folks also use non-contact guns for quick checks, generally understood as not really accurate but good for a relative reading that can be figured for actual cure temp.
