A 60 minute delay doesn't mean that it will take 60 minutes to tug the plane to the gate. Even if the tug does make it in 20 minutes (not unreasonable imo), there still is paperwork, fueling, loading bags and so on, all with little to no advance notice, and potentially getting pilots if the cancelled flight wasn't a DC9 as well.
OP didn't mention any cancellation. Do you have additional info?