Check your syntax.
If it looks like what you've posted it'll never work.
In the script it should read:
SetAccTime 0.1
playMusic "7thfly"
exit
Then, in your trigger, it should look something like this:
player addAction ["Slow Down Time", "YourScriptName.sqs"]
Just to add (you may have done this to save space) but in scripts if you put ";" (without quotations) it makes it void like "//" (without quotations. That's why I say that if it's laid out like that in your script, it won't work.