Stretching routine shouldnt be based on time, it should be based on how well you stretch, if your stretching well. Overtime you should become more flexible, if your not stretching well, it doesnt matter how long you take anyway.
I believe that every minute counts, meaning if you can only spare 1 minute of exercise on your day, then it counts. It's better to start small than not start at all.
I usually stretch about 10-15 minutes. It also helps to wake up in the morning. Get blood flowing and makes your body feel better overall. 🙂
I'd say about 5 minutes, enough time to stretch all parts of your body but not too long that it becomes impractical to keep it in your morning routine. When stretching make sure to take some deep breaths and be in the moment, it's a great way to start the day.