Very Computer

I am trying to refine a database to run a ski race. What happens is that
the start time is staggered for each racer, sometimes by 10,15 or 30
seconds. what I would like to be able to do is have the choice to add  
the appropriate number of seconds to time in the start time field. I am
using a format of 00:00:00   (hrs:min:sec) Any help or suggestions would
be appreciated(the less technical the better,unless you want to write it
for me!)Thanking you all in advance...
        Jac