In Ashtanga Yoga, the splits are already introduced in the standing postures. Utthita hasta padangusthasana and utthita parsvasahita are standing splits. Since all standing postures are also balance exercises, it doesn't exactly get easier. Over the years I have gotten better and better at balancing and staying long and steady in the postures. I haven't noticed a big change in flexibility. Since my sacroiliac joint injury, I no longer bend forward toward my leg.
I usually practice the splits (hanumanasana and sanakonasana) before these postures. Through the sun salutations, the body is already warmed up. First asanas are also practiced. Since the posture comes at the beginning of the series, the mind is still fresh. This allows for intensive practice. I don't think much of practicing the difficult postures at the end of a session. You are already exhausted by then. This makes injuries more likely.
Since I have been practicing the splits, both positions have improved.
The same positions occur again almost at the end of the middle part of the 1st series. Here the postures are called supta hasta padangusthasana and supta parsvasahita. Since one lies on one's back, all balance is eliminated. Using only the strength of the arms to push the leg toward the body or to the side to the floor allows only a gentle stretch. The progress is hardly perceptible. All my intensive splits exercises in which the weight of the body intensifies the stretch help to notice progress in the above positions. Without additional exercises not much happens.
For me, just supta hasta padangusthasana and supta parsvasahita are postures I use as a warm-up for my split exercises. They are the postures I practice when I have no energy to stretch more intensely.
Split exercise with a strap, April 2023
When you put a band around your foot and head, you feel how much more strength you have to intensify the stretch. You can press the foot of the leg lying on the floor against a wall to keep the leg stretched. There is a tendency for the knee to bend.
These positions of the first series made me work on the splits.
The splits will also appear in upcoming Ashtanga Yoga series. So it is a very good preparation for what is to come.
Everything that has to do with stretching takes time. Be patient with yourself.