What he said.
First, you don’t jump straight to double threshold workouts.
You start with double days - like an easy 30 minutes in the early morning on top of your regular workout in the afternoon.
Then you progress to multiple threshold workouts per week. And if all that is well tolerated, then maybe you do double thresholds.
Finally, you have to periodize your training. When is the idea time for double thresholds in your training plan???