ISM on the Peter Attia podcast says 75mins is a good duration at the 1.3 - 1.8 bla. intensity.
That’s would be a session where you would feel like you had trained but not that you were exhausted.
He says 3-4 times per week during the prep phase and maintenance of 1-3 when racing. He likes the polarised model.
He always says that carbohydrate is crucial and if glycogen is low then muscle damage and overtraining will occur.