FS2004 ASM tweeking

I am trying to make a snowplow and animate it so it runs up and down the runway. The animation is OK, but I try to tweek it to only run once and at a predeteremined time, f.eks at 0700 am. I have tryed to use Cat for fs2004, but only run into "run-time error '9'". How can I manualy tweek the .asm file, what should I wright and where in the file should I put it.

I am making it for FS2004. Can anybody help me.
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