So I ultimately decided that the atsunset configuration file will not have a list of commands, it doesn't belong in there. The configuration file will just have the lat/long pair for the location. Command line will be something like...

$atsunset 
     -f configuration file (default /etc/atsunset.xml)
     -o offset, default seconds but a trailing h, m or s will change the unit
     -d output useful debugging information and skip the file call to "at"

so an example would be

./atsunset plccommandline -a 00000001 -c on

which will execute "plccommandline -a 00000001 -c on" at calculated sunset

or (using the sister program)

./atsunrise -offset 30m echo good morning

which will execute "echo good morning" 30 minutes after sunrise