Start the practice now. Breathe in through your nose for a count of 5-7 and then breathe out, again through your nose for a count of 9-10. How many times you do this is up to you, but I would recommend at the very least 3x's several x's/day. If it's particularly stressful, add 1-3 times per day.
As you can see for yourself, it won't take you very long to do this.