I’m not a coach, but I would lean toward the second option for two reasons:
1. I had ADS going into my first training plan last year. I spent a couple months doing a variety of aerobic exercise (running/walking, cycling, unweighted box steps) below my initial AeT. By the time I started the actual training plan (12-week plan in preparation for Mt Shasta) I had shaved over a minute off of my running time and began to feel like the aerobic workouts I was required to do were less of a chore. It was motivating to see how much better I performed at my AeT test just two months later and that excitement helped fuel me through some of the more difficult weeks to come.
2.You can never have too much aerobic fitness. Building more aerobic fitness earlier will pay massive dividends when you get to the ME workouts.