Peer reviewed research shows a significantly greater benefit to repeated stretching versus a single stretching session, even if the total amount of time is the same. I find this to be true, and I'm stretching five or six times a day for five minutes each.
I also had terrible lower back pain in mid-2021, very similar to sciatica without the pain running down into my legs. It was so bad that after a three hour drive to a tennis tournament, I couldn't get of my car other than by crawling out onto the ground, and then I had to walk hunched over at a 45 degree angle to the tournament desk. I had to serve almost sidearm because I couldn't arch backwards. Still managed to get into the finals with the help of a lot of NSAIDs but had to default after one set. That killed my back for a while and so I set out to find what would work.
I discovered that it was most likely sacroiliac joint pain and I added a few exercises that have now totally cleared it up. I added floor-based twisting and cat-cow stretches. In the weight room, I did one-legged hamstring curls, and hip adduction/abduction resistance exercises. I had already been doing fully extended abdominal and back resistance training. Those new exercises seemed to allow my SI joint to regain the proper motion and within a month or so, the symptoms just entirely disappeared.