I think this may vary but here is what I think you need to try to accomplish when stretching.
When you initially go into a stretch position your muscles will react and tighten to prevent you from overstretching. This is an auto response. If you hold that position for about 30 seconds (again this will vary by person) the muscles will relax. You will then be able to stretch a bit more. You may reach a point where the muscles react again. Wait and maybe you go lower. You are now in a range of stretch that is actually increasing your flexibility. So overall you may need to be in a stretched position for 3 minutes.
I am not a professional, this is just based on my own experience in trying to achieve greater flexibility.
Holding a static stretch as a way of increasing flexibility is not the best choice. I use weight lifting to increase my muscle flexibility (and joint mobility).
Flexibility is a measure of how easy it is to lengthen a muscle passively through a range of motion. Mobility deals with the active movement of a joint through a range of motion. Active motion would not involve “holding” a muscle, rather it would involve continual movement (e.g., jumping jacks, skipping, etc.)
Believe it or not, a person can have great flexibility and poor mobility, which doesn’t seem to be the greatest goal.
Holding a position is called “static stretching”. The lengthening or extending of a muscle is a heck of a lot easier than the shortening or contracting of that muscle. When you lift weights you are doing both, but the contraction will be more difficult. That’s why doing a bicep curl is harder on the bicep on the way up, then on the way down.
As I personal trainer, if I have a client who insists on static stretching then I tell them to do it AFTER lifting weights and to hold any stretch only for about 15–30 seconds max and only 2–4 times. And to only stretch the muscles that were challenged when lifting weights.
When for a particular time period if you do not move your body to perform flexible tasks…… it becames STIFF which makes your body difficult to do regular things….

https://www.easyflexibility.com/