Hey Michele,
Although AdWords doesn't guarantee that script will run exactly at same minute every hour. They say that it all depends on he load on their servers. However, I have noticed that it all depends on the time at which you scheduled the script.
So, in your case you would have scheduled the script at a time like 11:27, so it runs at 27th minute of each hour. To make it run exactly at 8 AM, 9 AM and so on, you should remove the scripts schedule and then create a new Hourly schedule at exactly start of an hour.
This is not a guarantee but it works 99% of the time.
Regards,
Naman Jindal