Qualifying for Nations Marathon

When I run in a road race, will my time start when I cross the starting line, or when the gun goes off?  When I was a teenager, I used to run in the Manchester Road race.  It would take me almost 3 minutes to get to the starting line, from the 7:30 min/mile  line.

If I put myself at the 10:00/mile line in a race, and it it takes me more than 1 minute to get to the start, it will be significantly harder for me to qualify for the Nations Marathon.

 Please help ease my mind!