You do exactly the number of repetitions you are supposed to. You hold the stretches for exactly the right amount of time. You do your routine everyday, and and you do it first thing in the morning before anything else. Even before checking email.
But you're still stressed out. You still have anxieties that plague you during the day. You still can't get a great night's sleep.
It's probably because your mind is wandering while you workout.
Half of all mind-body regimens is in the mind. Doing the exercise is good for your heart, but thinking about that project your have to get done at work is bad for your heart. Stress-induced hormones increase your blood pressure and put you on high alert, making it impossible to relax as your thoughts spin around the source of your anxiety.
Put away the timer and start exercising for as long as it takes to feel relaxed. Go muscle by muscle, and move your mind into that part of your body. Picture the muscle and soft tissue like ice, frozen, but melting from your mind focusing on it, like heat from the sun.
Afraid you won't have time to get fully relaxed? Go to bed earlier and wake up earlier. Put yourself in a position where your schedule is wide open when you start stretching, so you can go as long as you need to without constantly checking the clock.
Eventually you should be able to feel each muscle by putting your mind there, and you should be able to consciously relax it with a deep breath.
Focus on your breathing too. Do whatever makes it easier for your to let go of your stress for this hour, or half-hour, each day. You don't need to solve your life problems or get any work done right now. Right now, you need to relax your body and mind.
Doing Tai Chi with a monkey mind is like not doing Tai Chi at all. Bring that energy down from your head to your center and cool off. A meditative mind is kind of like a sauna: you don't need to spend all day in there to feel the benefits. A little bit every day works too.