Ardha Matsyendrasana is difficult. It requires a few different aspects of flexibility, strength, and balance. You can just focus on Sirshasana, Sarvangasana, Paschimottanasana, and Bhujangasana for now. Work on doing some stretches to improve overall flexibility. Your overall balance will improve through the asanas. The asanas will be very hard at first.
You may start with two or three minutes at first, and even that can be difficult. The benefits of the asanas change with time. At first, you'll build a lot of willpower. Learn to concentrate your mind and hold the poses. You'll work your way up in time rather quickly if you are determined. Once you reach a point of strength and flexibility, the inverted poses become easy, so to speak. Concentration is very important.
It's a pleasure to see you practicing and growing.