I'm not asking for me. I'm just asking about the concept really. I'd say long would be 30-45 minutes of that type of effort.
OK, I got it.
Let me share my thoughts bellow.
Doing LT traing for 30-45 minutes twice a day is acceptable,but you must be careful. This could lead to a high level of fatigue in your body, and can cause injury or overtraining..
If you choose to do LT training for 30 minutes twice a day, it would be more specific to a HM race. You might require around 4 days of recovery time.
On the other hand, if you opt for LT training for 45 minutes twice a day, it would be more specific to a FM race. This might necessitate about 7 days of recovery time.
Thus, if you opt for LT training twice a day, your weekly mileage will inevitably decrease. This is because you'll need more time for recovery.
Above is LT training twice a day, it was me who read it wrong.
So, when it comes to LT training twice a week, my answer is: no problem!
IMO, there is no reason you can't just do long thresholds(30-45 min) twice a week.