Early breathlessness in a race or in training occurs due to the oxygen supply not at first keeping up with the body's needs. This can, of course, be mitigated by the warm up, which inures the body to the demands it will be encountering.
For performance to be enhanced there is obviously a time limit between cessation of warm up and the main activity. Stopping the warm up 30 minutes before the race or session simply will not work. It is recommended that the time span should not exceed 5 minutes, and indeed in a race situation one should be jogging on the spot on the line.
I recommend the following before a race:
Start 40 minutes before the race with 15 minutes of easy, graduating to steady pace running. Then a few gentle 'unkinking' exercises to loosen any tense areas. Next 3x100m stride outs followed by a 60 second quite hard effort 10 to 15 minutes before the start of the race. Gentle jogging and walking until the start.
Before a training session: 10 minutes easy 'unkinking' exercises and 3x100m strides.TThese measures will ensure that you are well prepared for your race or training session.