This was at Terminal 2 (I think) and the flight arrived late at night. So it took me 25 minutes (to the car park not the train station), please remember this is my experience and it could take longer for you. You have to take into account: flight delays, baggage delays, queues, crowds, getting lost etc.
the first trimester is from week 1 to the end of week 12 the second trimester is from week 13 to the end of week 26 the third trimester is from week 27 to the end of the pregnancy source: http://kidshealth.org/parent/pregnancy_calendar/pregnancy_calendar_intro.html.
The first trimester of pregnancy lasts for about the first three months of pregnancy, and is usually the time when a woman realizes that she is pregnant. During the first trimester a woman may experience nausea, extreme tiredness, headaches, mood swings, and several other symptoms.