Possibly a silly answer, but a thing I've broken my head on previously myself.
Could it be that your percent is a value from 0 to 1 (rather than 1-100 - usually programs see it as 0-1 even if they display it at 0 % to 100%) ?
So you should be looking for if [Percent Ontime] > 0.9 ?
If that doesn't answer the question, can you share some of your data ?
That did the trick - now everything works perfectly. Yayyyy!