For several years I had issues with hip tendinitis that were caused by overuse, mostly hiking up hill with heavy packs. The short stretches they taught me in physical therapy failed to resolve it. My doctor prescribed meloxicam but that only masked it. Eventually I was desperate enough to try a cortisone shot which was effective short-term, but the pain came back.
With nothing left to lose, I started a 21-day hip opening program I found online. The holds are long, about 5 minutes each, and it was a total of abut 20 minutes a day. It was difficult (I was very tight) but the improvement in flexibility was noticeable, so I kept it up and in a short time the pain went away completely. It has never come back. It also helped resolve lower back issues and knee pain when running, and allowed me to move better when climbing.
So, I would stick with it. I also find foam rolling is great after exercise to reduce soreness the next day.