On-time performance of UA989 seems good enough. It's on-time around 80% of the time (actually, it's usually coming in early). And when it's delayed, average delay is 30 min with a standard deviation of 25 min. Maximum delay observed according to the free flightstats data was 82 min.
So, given you're delayed (happens 20% of the time) there's only a 15% chance the delay will be greater than 55 min. 50% of the delayed flights will be less than 30 min late. 85% of the delayed flights will be less than 55 min late. I've simplified here and assumed delays are normally distributed.
On GF, I also see the option to route through ORD, being on a flight that comes in at 05:45.